New York (CNN) After 27 hours of surgery, twin boys Anias and Jadon McDonald -- born joined at the head 13 months ago -- began a new life apart on Friday.

The round-the-clock operation at the Children's Hospital at Montefiore Medical Center in the Bronx began Thursday morning and ended Friday. The separation procedure itself lasted 16 hours, followed by more hours of surgery to rebuild their skulls and make them whole.

Jadon was the first of the boys to be finished. He was wheeled out of the operating room around 7:40 a.m. on a stretcher, his perfectly shaped head wrapped in white gauze.

He was taken on an elevator to the pediatric intensive care unit on the 10th floor, where he was reunited with his parents, Nicole and Christian McDonald.

"My boy," Christian said with tears in his eyes.

Nicole bent over in tears.

More than five hours later, around 1 p.m., surgeons finished operating on Anias, and he was brought to the 10th floor unit -- where the family was finally reunited.

Photos: Conjoined twins separated: New life, apart Anias, left, and Jadon McDonald were born conjoined at the head, something only seen in 1 out of every 2.5 million live births. They were separated in a 27-hour surgery at the Children's Hospital at Montefiore Medical Center in New York in October. Hide Caption 1 of 24 Photos: Conjoined twins separated: New life, apart Nicole and Christian McDonald talk with Dr. Sanjay Gupta in the family waiting area on October 13 as a team worked to separate Jadon and Anias. "When we sent them off this morning, to me, I felt at peace with it and just ready to handle what comes after," Nicole said. Hide Caption 2 of 24 Photos: Conjoined twins separated: New life, apart Dr. James Goodrich Goodrich, left, leads a surgical team as they prepared to separate the twins. "Failure is not an option," Goodrich told the team as they got started. Hide Caption 3 of 24 Photos: Conjoined twins separated: New life, apart Hide Caption 4 of 24 Photos: Conjoined twins separated: New life, apart The twins' surgery was Goodrich's longest craniopagus surgery. It's meticulous, tricky and complex: A single cut too deep can lead to catastrophic bleeding. Hide Caption 5 of 24 Photos: Conjoined twins separated: New life, apart Goodrich's team worked more than 16 hours just to separate the boys, and each continued surgery individually afterward. Hide Caption 6 of 24 Photos: Conjoined twins separated: New life, apart Newly separated twins Anias, left, and Jadon in surgery at the hospital. Goodrich informed the family of the successful separation at about 3 a.m. October 14. "Well, we did it," he told them. When it was official, the room burst into spontaneous applause.

Hide Caption 7 of 24 Photos: Conjoined twins separated: New life, apart Jadon recovers in the pediatric intensive care unit shortly after the surgery. Hide Caption 8 of 24 Photos: Conjoined twins separated: New life, apart Anias returns to his room after his head dressing was changed. Hide Caption 9 of 24 Photos: Conjoined twins separated: New life, apart Jadon stretches his arms in his room within the hospital's pediatric intensive care unit. Anias rests in a nearby bed in the same room. Hide Caption 10 of 24 Photos: Conjoined twins separated: New life, apart Anias, left, stares at Jadon for the first time since the surgery that separated them. Hide Caption 11 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald, right, and her mother, Chris Grosso, with Anias in mid-November. Anias had to have his skull cap removed due to infection, but doctors say they are still pleased with his recovery. Hide Caption 12 of 24 Photos: Conjoined twins separated: New life, apart Anias, left, and Jadon lie in a red wagon at the Children's Hospital at Montefiore Medical Center on December 13 as they prepare for the next stage of their journey, two months after their surgery. Hide Caption 13 of 24 Photos: Conjoined twins separated: New life, apart The family was headed to the hospital's banquet hall on December 13, where surgical and pediatric intensive care staff members were gathered for a farewell party. Hide Caption 14 of 24 Photos: Conjoined twins separated: New life, apart Dr. Oren Tepper, the twins' lead plastic surgeon, holds a thank you gift from the McDonald family presented to him at the farewell party. Hide Caption 15 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald holds Anias as his twin brother, Jadon, sleeps in the bed to the left. The twins' older brother, Aza, watches television at the hospital from one of the boys' beds shortly before they left for rehab. Hide Caption 16 of 24 Photos: Conjoined twins separated: New life, apart Jadon, left, and Anias McDonald look up at hospital staff as they leave their room at Montefiore Children's Hospital in New York. Their older brother, Aza, proudly sits at the front of the wagon. It was mid-December and they were headed to rehab. Hide Caption 17 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald pushes a stroller with Anias as her husband Christian pushes Jadon down a hallway on June 14 at Blythedale Children's Hospital in Valhalla, New York, where the boys have been rehabilitating. Hide Caption 18 of 24 Photos: Conjoined twins separated: New life, apart Anias plays with a toy while laying on a mat in his room at Blythedale Children's Hospital. Hide Caption 19 of 24 Photos: Conjoined twins separated: New life, apart Jadon eats small snacks and drinks from a sippy cup on his own, major progress since he first moved to rehab. Hide Caption 20 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald plays with her son Anias as Christian McDonald holds Jadon on a playground outside Blythedale Children's Hospital. Hide Caption 21 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald holds Jadon while looking over discharge information on September 1, as they prepare to leave the rehab facility and head home as a family for the first time. Hide Caption 22 of 24 Photos: Conjoined twins separated: New life, apart Nicole McDonald takes Anias into the family's new house for the first time with his older brother, Aza. Hide Caption 23 of 24 Photos: Conjoined twins separated: New life, apart Christian McDonald holds his son Anias as Nicole McDonald checks on Jadon at home with the family dogs, Taz and Tyson. Hide Caption 24 of 24

The surgery was led by Dr. James Goodrich, considered the leading expert on what's known as craniopagus surgery.

It marked the seventh and longest separation surgery performed by Goodrich -- and just the 59th craniopagus separation surgery in the world since 1952.

Nicole and Christian had to make an excruciating decision, opting for the procedure even though it carried major risks, including the possibility of death or long-term brain damage for one or both boys. But not to operate also carried risks: 80% of twins joined at the head die of medical complications by age 2 if not separated, studies show.

Goodrich informed the family of the separation around 3 a.m.

"Well, we did it," Goodrich said.

On her Facebook page , Nicole wrote: "TWO SEPARATE BABIES!!!...and yet I ache with the uncertainty of the future. I didn't cry until the surgeons left the room. I was barely able to even utter the words 'thank you' because of the pit that still sits heavy in my stomach. We are standing on the brink of a vast unknown. The next few months will be critical in terms of recovery and we will not know for sure how Anias and Jadon are recovering for many weeks."

The moment capped an end to an agonizing wait for the boys' parents.

The McDonalds and Montefiore hospital invited CNN to document this remarkable and rare journey of Jadon and Anias, allowing CNN exclusive access into the operating room throughout the procedure.

Yet before Nicole and Christian learned their boys were now two individuals, Thursday was a day of high emotion and high stakes, of anxious parents and calm medical professionals. It was a day of uncharted territory and amazing, one-of-a-kind surgical activity.

And amid it all were two infants -- beautiful boys with deep brown eyes and a shared swirl of hair at the top of their foreheads. They came into the world together, and became two individual boys overnight.

The parents' worries extend beyond the surgery; they wonder what happens in recovery.

'I feel good'

Dr. Goodrich stands in Operating Room Number 10. It's a drab off-white, and empty of people. Two operating tables sit in the middle of the room, abutted together. A 3D replica of the boys' heads sits between them.

It's 6:52 a.m.

The doctor began his day by skipping breakfast and enjoying a single cappuccino.

It's been 12 years since he last separated twins conjoined at the head at Montefiore. That was his first ever craniopagus surgery, and he's learned much since then, performing five other separation surgeries around the world, including Syrian twins in Saudi Arabia earlier this year.

Prior to the mid-1980s, it was accepted medical practice to sacrifice one child on the operating table to save the life of the other. Many times both babies died. If one child made it through surgery, he or she often suffered debilitating brain damage.

Dr. James T. Goodrich in his office at the Children's Hospital at Montefiore.

Goodrich has pioneered the field. He established the practice of performing the separation of craniopagus twins in several shorter stages, instead of one single operation lasting more than 50 hours. The McDonalds have had three previous operations, each resulting in progressively more separated brains. Today is the fourth and final stage. None of Goodrich's conjoined twins have died during the operation. His mantra: "Take it easy and slowly and carefully."

His surgical cap embodies that philosophy: It's decorated with turtles.

"Don't change what works," he says. "Ready to go."

Within minutes, he and Dr. Oren Tepper -- the plastic surgeon charged with reconstructing the boys' skulls and stitching their heads back together -- go to the 10th floor to a corner room where Jadon and Anias are resting with their family.

The doctors exchange pleasantries with Mom, Dad and other family members who crowd the room. Asked how he's feeling, Goodrich breaks out into a James Brown-like jig. "I feel good," he croons.

At 7:12 a.m., the boys are wheeled out of the room. Their older brother, Aza, lies with the twins on the stretcher as they're taken down an elevator and through a phalanx of hallways toward the third floor operating room.

"Open door," Aza says.

It's time to say goodbye. Against his will, Aza is taken off the stretcher. "Babies, babies," he says, reaching toward his brothers.

Mom and Dad kiss their boys bye. "We'll see our two boys later," Christian tells Nicole.

Nicole scoops up Aza and cradles him. The three walk away. The twins go straight into the OR.

It's 7:18 a.m.

Photos: Conjoined twins at the head prepare to be separated Anias and Jadon McDonald were born conjoined at the head on September 9, 2015, via an unscheduled C-section. "They were normal little boys, like any other two little babies you would see," said their father Christian McDonald, "except for being conjoined." Hide Caption 1 of 13 Photos: Conjoined twins at the head prepare to be separated "Don't worry," Nicole McDonald said to her husband when she told him about being pregnant with conjoined twins. "We'll figure it out." Hide Caption 2 of 13 Photos: Conjoined twins at the head prepare to be separated "I can't wait to see them as two separate little boys," said Christian. "That's what excites me the most. I really just want to know my boys." Hide Caption 3 of 13 Photos: Conjoined twins at the head prepare to be separated The parents describe Jadon, left, as the rambunctious one, and Anias as the contemplative one who loves listening to his mom read. Hide Caption 4 of 13 Photos: Conjoined twins at the head prepare to be separated When the boys were younger they could be transported in a kid's wagon, seen here when they were three months old at Rush University Medical Center in Chicago. Hide Caption 5 of 13 Photos: Conjoined twins at the head prepare to be separated Anias stares into the camera. His gaze is so captivating, his mother says, "it's like he looks at your soul ... He's just a silent warrior. He's sweet and strong." Hide Caption 6 of 13 Photos: Conjoined twins at the head prepare to be separated Nicole and Christian McDonald at their home in the Bronx. Hide Caption 7 of 13 Photos: Conjoined twins at the head prepare to be separated The boys also have a 3-year-old brother, Aza. He's grown more quiet in recent weeks ahead of the twins' surgery. Hide Caption 8 of 13 Photos: Conjoined twins at the head prepare to be separated The boys share 1.5 to 2 inches in diameter of brain tissue. The surgery to separate them could take as long as 20 hours. Hide Caption 9 of 13 Photos: Conjoined twins at the head prepare to be separated Only one out of every 2.5 million live births results in twins conjoined at the head. But 80% of them die of medical complications by the age of 2 if not separated. Hide Caption 10 of 13 Photos: Conjoined twins at the head prepare to be separated Dr. James Goodrich, here with Nicole and the boys, is the most experienced craniopagus neurosurgeon in the world. Separating Anias and Jadon will mark his seventh separation surgery. He's consulted on 13 other conjoined twins. Hide Caption 11 of 13 Photos: Conjoined twins at the head prepare to be separated New 3D imaging and mapping has made this surgery unique and allows the surgical team to see exactly what to expect when they make the first incision. "There's no more guessing," said Goodrich. Hide Caption 12 of 13 Photos: Conjoined twins at the head prepare to be separated Christian and Nicole pose on the bed with their twins. Anias is on the left, while Jadon is facing his father. Hide Caption 13 of 13

'Failure is not an option'

In a waiting area off the operating room, Goodrich and Tepper huddle with neuroradiologist Joaquim Farinhas.

Farinhas shows off a three-dimensional replica of the boys' brain vessels that can be pulled apart, revealing exactly how they are fused together. The boys share about an inch-and-a-half diameter of brain tissue.

"This is what I wanted you to see," Farinhas says, "which is something that is soft and you can actually poke in and cut through."

Goodrich studies it for a bit before saying, "Ready to rock 'n' roll."

"Absolutely," Farinhas says.

"Failure is not an option," Goodrich replies. It's 7:22 a.m.

For the next two hours, the boys are prepped for surgery. The place is a hub of activity, but of steely calm. The boys drift to sleep under anesthesia.

At 9:27 a.m., plastic sheets are placed over their naked bodies, followed by blue surgical drapes. Moments later, their heads are wiped clean and Tepper takes a black marker and outlines incisions from the three previous surgeries.

At 9:36 a.m., neurosurgery nurses Bindu Peter and Treshia Alex conduct what is known as a "timeout" -- a required protocol before surgeries. They name both patients on the tables and the operations taking place this day, October 13, 2016.

"We are doing craniopagus separation, fasciocutaneous scalp flaps, removal of expander, cranioplasty with bone graft, possible skin graft or use skin substitute, adjacent tissue transfer scalp, possible insertion of tissue expanders, possible insertion of wound closure device," Peter says.

"Correct."

More than 20 people in the room -- surgeons, doctors, nurses, staff -- say their names and titles.

"How long will the case take?" says Peter.

Goodrich: "Long."

"Any patient-specific concerns?" the nurse asks.

"Bleeding," one voice says.

"We have cross-matched two units of blood. It is in the blood bank," Peter responds.

"Correct," Goodrich.

There's some small talk, then Goodrich motions with his hands to Peter, as if to say you're forgetting something. "Final line?" he says.

"May the surgeon do a wonderful job," one doctor says.

Others chime with "A wonderful job!" and "Good luck!"

Goodrich flashes a thumbs up: "Thank you."

It's time to operate. Tepper makes the first incision at 9:45 a.m.

Dr. James T. Goodrich holds a 3D model of the McDonald's twins in his office at Montefiore.

'The easiest part is done'

The next several hours are a whir of activity. In the three previous surgeries, the surgical team added tissue expanders to stretch the skin to make sure there was enough to cover their new skulls. Surgeons also separated some of the veins to make way for today's final separation.

Mom and Dad eat breakfast with their extended family and take Aza to a nearby park. Nicole is relieved to have Aza to look after because chasing after him keeps her anxiety in check.

Christian goes to a dollar store and buys packs of thank you cards. He and Nicole spend more than an hour writing personal notes to their closest friends and family for helping them get this far.

The family holes up in the Caregiver Support Center, two floors and two corridors away from the operating room. Shortly after CNN's first story about the family appears Thursday morning, Nicole and Christian start getting swamped with messages from friends and strangers alike. They monitor the hashtag #JadonAndAnias and watch as thousands of dollars in donations pour into their GoFundMe page.

They're buoyed by the messages of support from people as far away as the Philippines and Germany. They say their faith is renewed in mankind -- that it's a nice break from sordid headlines and the hotly contested political season.

Humanity wins.

"Everybody is really showing how much they love these boys," Christian says. "I didn't realize how many people out there have so much good in them and how much they want to help."

Nicole had quit her job as a pediatric physical therapist to care for the twins. She reads notes from mothers whose children she once cared for, including one who nicknamed her "Miracle Worker." On her Facebook page, that mother writes, "Nicole is a Miracle Worker and now we're seeing miracles worked in her life."

"They're all just so heartfelt," Nicole says.

By noon, the surgical team has taken out one tissue expander and removed some temporary plates that were inserted in the earlier surgeries to hold bone back.

At 12:04 p.m., it's time to turn the boys to get to a new area to cut -- a delicate maneuver that requires all hands on deck.

"1, 2, 3, lift!" a team member says.

Jadon's shoulders rotate 45 degrees. They adjust Anias into a similar position. Tepper remains calm, continuing his work.

Goodrich stands and turns away from the table. He grabs a nearby 3D replica of the boys' conjoined skulls. A wine connoisseur, he studies it, mulls it over like a fine chardonnay. He's facing two large screen televisions. One shows a live view of the surgery going on behind him. The other provides images of three-dimensional computer models of the boys' veins, arteries and other brain matter.

Soon, Goodrich returns to the table. Working diligently with him is Tepper and three other surgeons: Dr. Rani Nasser and Dr. Ajit Jada, both chief residents of neurosurgery, and Dr. Carrie Stern, senior resident of plastic surgery.

The high-pitched sounds of tiny cutting instruments pierce the air. A smell, not unlike that of having a cavity filled at the dentist's office, permeates all around.

At 1:55 p.m, more than four hours into the surgery, Goodrich turns around and says, "The easiest part is done."

Fifteen minutes later, a chunk of skull is removed. No time to rest. The surgical team presses on. They take out a second tissue expander shortly before 3 p.m.

Soon after, Goodrich sneaks off for two slices of pizza in a quiet, secluded room in the hospital. Nineteen minutes later, he heads back to the operating room.

'Land of the unknown'

Nicole and Christian bide their time with family. Aza bounces off the walls. Grandparents and others pitch in to keep the 3-year-old from driving their mom and dad too crazy.

Mom enjoys the distraction. They get occasional updates on the surgery from a nurse practitioner for pediatric neurosurgery. Christian wishes they'd get more news on how it's going.

The family members wear white T-shirts Nicole designed. The front of the shirt says Anias with its Hebrew meaning, "God has answered," and Jadon, "God has heard." An infinity sign -- often used as a symbol for conjoined twins -- goes across the middle.

Nicole made the shirts to try to raise a few bucks. Soon, she had 200 orders. The family ended up selling 1,000.

"I'm gonna hug my wife," Christian says, pulling her tight and holding her.

The time now is 4:46 p.m.

The day has been a whirlwind since saying goodbye to the boys nine hours earlier.

Nicole had never even posted a photograph depicting the boys as conjoined until a month ago.

She always took tight shots of each boy's face to show them as individuals. But she knew she wanted to speak to CNN and needed to be brave to "better prepare myself for exposing my children to the world."

So, she posted one photo of the boys conjoined on Facebook and then another on her GoFundMe page. "I said, 'OK, I'm getting real brave.'"

"The response was beautiful," she says.

And now, this day, her boys' day of separation -- a symbolic "second birthday" -- the outpouring of love has been awesome.

"The babies steal the show," Christian says.

Nicole: "It's their eyes."

"We would have it no other way, though," Christian responds.

It's now past 5 p.m. As the day progresses, they know their anxiety will intensify. Their boys have gone through the three prior surgeries, and they know the doctors are still making their way through basically undoing those three surgeries before going into the final separation phase.

"I call it the land of the unknown," Nicole says.

Yet their worries extend beyond their boys surviving today. They wonder what happens with recovery. Will they have seizures? Will they suffer heart failure? How long will they be in intensive care?

Despite their worries, Nicole says, "When we sent them off this morning, to me, I felt at peace with it and just ready to handle what comes after."

Dr. Goodrich and Nicole McDonald with the twins before surgery.

The most critical phase

Shortly before 9 p.m., the operating room intensifies. The surgeons have reached their most critical phase: They must separate the shared blood vessels between the two boys. Veins are very thin walled, and one section of Jadon and Anias' brains are intricately tied together, much more so than originally believed.

A single cut that goes too deep can lead to catastrophic bleeding.

Neuroradiologist Joaquim Farinhas stands in front of the screen displaying the 3D computer model. He calls Dr. Ajit Jada over from the operating table and points at the cluster of veins. Farinhas dispenses advice. Jada returns to the table.

"Be very gentle with Anias' side," Farinhas calls out to the surgical team.

Tepper, who had taken a brief break, returns to the table.

"It's a bear," says Farinhas.

"This is the most important part," he explains, "because the vessels are so delicate and they're so complicated. It's almost a lake of veins that they're trying to negotiate. It's pretty amazing."

The surgical team has to figure out: How do you tie it off safely? How do you separate it? Should we proceed?

At 9:18 p.m., Goodrich says, "We just closed off the sagittal sinus."

"That chardonnay is on the way," quips Farinhas.

A note of levity amid the intensity.

The last stitch

Seconds tick off into minutes, which turn into hours.

The surgery is meticulous, tricky, complex. And that's an understatement.

At 1:18 a.m., Tepper, the plastic surgeon, steps to a nearby metallic table and takes a special saw to split a removed skull piece into two. Those two pieces will be used for the boys' new skullcaps.

Goodrich and his team continue to work away toward the moment of separation. At about 1:40 a.m., he sits in a seat next to the operating table with hands crossed, as if admiring the work. Moments later, he stands and dives right back into surgery.

At 2:10 a.m., Goodrich says, "One more inch."

"We're ready. You ready?" one surgeon says.

"Yep," Goodrich says.

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It's a badge of honor as to who gets the last cut when separating conjoined twins.

"The last stitch," Tepper says. "Who wants it?"

The only woman surgeon at the table, Dr. Carrie Stern, makes the historic last cut, at 2:11 a.m.

"We are official," Goodrich says.

The room bursts into spontaneous applause.

After nearly 16½ hours, the boys are separated.