Lexie Stewart can sing like an angel but her mom can't even carry a tune — just one of many mysteries for the 15-year-old girl who will likely never meet the man who provided half her genes and many of her most notable traits.

Then, earlier this summer, Lexie met two of her half-siblings for the first time, and everything started to make sense.

The meeting took place at a beach house on the New Jersey shore, where three teens and five moms spent a week and a half getting to know each other and forging a new kind of family.

The mothers were perfect strangers, drawn together because they happened to choose the same donor sperm from a company in Atlanta.

Kim Stewart with her daughter, Lexie. (Julie Ireton/CBC)

Lexie was brought up by her single mom, Kim Stewart, an Ottawa public servant who always told her only child she'd moved heaven and earth to bring her into the world.

In her desperation to have a baby, Stewart didn't spend much time worrying about her future child's inevitable curiosity about the origin of her natural talents, her blond hair or her almond-shaped eyes — or if there was anyone else out there who shared her DNA.

But as Lexie grew older, her curiosity grew, too.

'I wondered, do they look like me?'

About a year ago, Lexie logged on to the Donor Sibling Registry, a privately run Colorado-based online service that helps unite donor-conceived children with half-brothers and half-sisters around the world.

All they need to register is the unique donor code, a unique series of letters and numbers contained in the donor file their mothers received when their children were conceived.

With that code in hand, Lexie quickly discovered she had at least 14 half-siblings.

Just like that, she was no longer an only child.

"I was just so excited because I've always wanted to have siblings and finally, there's all these families. I'm reading their biographies and learning about them and what they look like. I wondered, do they look like me?"

They do. Most of the donor's offspring have blonde hair and blue eyes, and all have a love of and talent for music.

"We know that he's a music teacher, which is pretty funny," said Lexie, who specializes in vocal performance at her arts high school.

'Like my birthday 10 times over'

Around the same time Lexie was starting to explore the donor registry, Briley Lewis, more than 2,300 kilometres away, was embarking on his own quest to find blood relatives.

Briley Lewis wore a special shirt to celebrate the meeting with his half-sisters. (Julie Ireton/CBC)

Briley plays trombone, piano and cello, but like Lexie, he said he's the "lone wolf" when it comes to any musical talent in his home. At 16, Briley is the pride of a loving two-mom family in a conservative Kansas community.

He said his whole world changed when he signed on to the donor registry.

"I was really overwhelmed ... When I got on the website and saw all those entries, it was like my birthday 10 times over," says Briley.

He was the first to exchange messages with Lexie. Kim Stewart remembers her daughter's shock and excitement.

"She said, 'Mom, my brother sent me an email,'" recalls Kim. "And it was just the greatest. We were both bawling."

There was more to come.

Their 1st meeting

In New Jersey, 15-year-old Katee Kemether and her moms — both lawyers — were also scrutinizing the Donor Sibling registry. Coincidentally, they finally decided to sign on within a couple of days of Lexie doing the same.

They'd later find out the two half-sisters had been born just days apart. In fact, the girls could almost pass for twins, with the same round faces, the same almond-shaped eyes, straight blond hair and a shared ability to arch their left eyebrow.

The three half-siblings started messaging, exchanging emails, then communicating via Facetime. They formed an immediate bond, and soon began hatching a plan to get together with their mothers.

Even though they'd seen each other's faces on their smartphones and laptops, their moms still blindfolded the kids for their first encounter. When they were led into the room and the blindfolds came off, they all screamed and hugged, ecstatic to finally meet.

Three children conceived from the same donor sperm see each other's faces for the first time. 0:42

"It was just so freaky to look at Lexie," said Katee.

Briley agreed. "When you see them in the flesh, it's a lot of staring. It's like, wow,"

Getting to know each other

Lexie Stewart holds a childhood photo of the anonymous sperm donor. (Supplied) Katee showed her half-siblings around, taking them kayaking and biking. They went to a show in New York City, and watched the Fourth of July fireworks from the boardwalk.

"I know there was some concern about how we're going to live for a week with these people we've never met before, but it's been fabulous," said Noreen Kemether, one of Katee's moms, who hosted the gathering at their beach house.

Briley's mom, Barb Lewis, said her son always felt like he was missing something.

"It would come up when he was younger. He'd wish he had a dad."

Instead, he had a dog-eared donor file that contained an essay written by the anonymous donor, a photograph taken when he was about seven or eight years old, and other biographical tidbits.

"Now he has a family, I mean a real family ... To him, this is his family," Lewis said.

Lucky it turned out well

The moms all admit they had reservations about joining the registry, and about the meeting. They know they were lucky with the way it all turned out.

"I just didn't know what we might be embarking on, kind of opening up that door," said Kim Stewart.

It's a sentiment shared by Katee's mom, Noreen.

This map shows the current locations of 14 of the children who were conceived with the anonymous donor's sperm and who later joined the Colorado-based Donor Sibling Registry. Pink indicates female offspring, blue indicates male and grey indicates unknown gender. (CBC) "I wanted to make sure that they were comfortable with it and comfortable with themselves."

The teens have been in touch with some of the 12 other half-siblings registered, but have found most are younger, and some have several brothers and sisters of their own. None of them have formed the same close bond as Lexie, Briley and Katee.

They know, too, that there could be many more half-siblings out there who haven't joined the registry.

Their donor remains anonymous, and hasn't signed on to the voluntary registry either. Lexie said she doesn't care if she ever meets him, but Katee thinks it would be cool.

Briley said the void he once felt because he didn't know a father has now been filled — by his new sisters.

"If you'd asked me a few years ago, I'd say I'd really need to meet him. Now I feel better, and having two siblings that share the situation makes it a lot easier."