Kate holds a 1990s family photo showing her as Bill, with Linda and their children Matt and Megan. Credit:Washington Post Yet before leaving for the hospital that February morning, Linda had to make sure. "You still want to do this?" she asked. "Absolutely," her spouse answered. A short time later, a smiling, even ebullient patient lay propped up in bed, awaiting the final pre-op questions. The name on the medical file passed among the staff already read Kathryn Rohr. Kate for short.

Kate (formerly Bill) Rohr talks with her doctor Marci Bowers (left) after surgery. Credit:Washington Post "And your goal today?" a nurse asked. "Turning an outie into an innie," Kate answered, laughing. Kate Rohr has finally become a woman, undergoing sex reassignment at the age of 70. Credit:Screengrab Linda, hovering nearby, absent-mindedly smoothed the bedsheet. Nothing to do now but wait. Finally, she sat down by the door, clutching Kate's clothes and their two purses. She was the only one in the room visibly nervous.

Three years earlier, sitting at the dining-room table at their home in Fort Bragg, California, it was her husband who'd been nervous, unsure of what was about to happen. Bill Rohr (right) with his father-in-law in the early 1970s. Credit:Family From the time he was little, he began telling his wife, he had believed he was a female in a male body. It wasn't about the clothes or toys, he explained. He'd never yearned to be a princess or ballerina. He just couldn't understand why everyone around him treated him like a boy instead of a girl. Kate (left) with Linda at home. They've been married for nearly 48 years. Credit:Washington Post

"Something just told me, I'm the other half of the population," he said. To a bright child with a gift for engineering and logic, this mystery of mistaken gender had been something to puzzle over but never question out loud. It certainly couldn't be shared - not with his parents or his brothers or his friends. Even if they accepted it, what could anyone really do? Kate (formerly Bill) Rohr chats with a nurse prior to surgery. Credit:Screengrab So he endured, through a childhood that was confusing and a puberty that was torture. He felt hormones "ravage" his body, turning him unmistakably male. He avoided looking at himself in a mirror, even to comb his hair. But in every other way, he tried to be the best, most typical boy he could be. Growing up in the suburban hamlet of Fanwood, New Jersey, he played sports and studied hard, and even though he believed God was deaf to his prayers, he dutifully sat next to his parents in church every Sunday. The days ticked by, and the boy became a man. He married his hometown sweetheart at age 20, graduated from Princeton and went on to earn a master's degree in mechanical engineering. Medical school put him on the path to becoming an orthopedic surgeon, then a business executive, too. Where other doctors worked 12-hour days, he worked 18. He gave seminars around the world, patented new tools for knee replacements and started a family.

Linda caresses Kate's hand after surgery Credit:Washington Post The present became the past, and the young man became middle-aged, but he never stopped thinking about what he'd buried so long ago, never stopped wondering about why and how and what if. At the same time, he knew that if his secret was ever unearthed, it would cost him everything he cherished. There was no map to happiness in this world. How could he know the woman whose love he most feared losing would be the person who would save him? A glimmer of hope Bill Rohr and his family - from left: Linda, Matt and Megan - long before Bill became Kate. Credit:Screengrab It was a single-column story, low on the front page of the New York Times. College sophomore Bill Rohr picked up the paper and noticed the headline immediately. The first sentence nearly sent him reeling: "The Johns Hopkins Hospital has quietly begun performing sex change surgery."

The date was November 21, 1966. The article mentioned Harry Benjamin, an endocrinologist and sexologist who led a foundation spearheading the effort to have transsexuals - a term Benjamin coined - treated as medical, not psychiatric, patients. His book, The Transsexual Phenomenon, had just been published. Two days later, Rohr rode a train from Princeton into New York to buy it. "I was flabbergasted," Rohr recalled recently. "It described me exactly. It also provided evidence that this was a medical condition and that it was immutable." All of it was revelatory, helping him realise he wasn't a freak. But that understanding did little to blunt the agony and fear that continued to hold him hostage. Respite from the relentless struggle to be something he was not came only in the library, where late into the night he could turn his mind to books like Benjamin's. The physician's experiences had convinced him that there were untold numbers of people whose psychological, emotional and mental belief of being male or female was opposite to their sexual anatomy at birth. Benjamin thought genetics and prenatal conditions probably played a significant causal role, but because the 1960s and '70s were the heyday of behaviourism in psychology, nature took a back seat to nurture, as that New York Times article made clear:

"Psychiatrists believe that transsexualism is caused by prolonged conditioning early in life, perhaps within the first three years. Some cases, in which a mother wanted a daughter instead of a son and raised her child accordingly, seem obvious, but the origin of others is obscure." Today, an overwhelming number of doctors and scientists dismiss the idea that environment, or behavioural conditioning, causes a person to be transgender. Most agree that sexual anatomy, sexual orientation and gender identity are the result of three distinct developmental processes in the fetal brain. Yet only recently have researchers begun to tease out how that brain is masculinised or feminised. Hormones, it appears, play an essential role. "As one patient once told me, sexual orientation is who you go to bed with, gender identity is who you go to bed as," said Norman Spack, a pediatric endocrinologist and co-founder of the Gender Management Service at Boston Children's Hospital. Bill Rohr definitely knew the difference. He felt female, believed he was female, but he was also attracted to women - which is why the second time in life he crossed paths with Linda Sue Schwingel, he did everything he could to hold on to her. They had lived only a mile apart in Fanwood and attended the same public high school. Bill even took Linda to their freshman prom. But six more years went by before they truly got together. Linda had just graduated from junior college, and one day Bill happened to drive by her house. He noticed Linda's parents sitting on the porch. He drove by the house a second time, then a third. By the fourth time, Linda's astute mother had alerted her daughter, who was now outside, too.

Rohr stopped, and love bloomed. "He was my Prince Charming," Linda said. "He just swept me off my feet. And we've had fireworks ever since." Six months later, they were engaged. Six months after that, they were wed. "Marrying Linda was the best decision of my life," Rohr said. But it also foreclosed the chance of ever transitioning to being female. Rohr was reminded of the consequences often, including once in medical school at Washington University in St Louis. During his psychiatry rotation, he watched a 20-something patient undergoing electroshock therapy to "cure" him of his transsexuality. Straps restrained the young man's head, chest, waist and legs. A rubber guard protruded from his mouth. With one brief jolt of electricity, the patient's head and neck arched, his mouth clenched. For at least a minute, his body shuddered through the seizure.

Rohr was horrified, then furious: "They were trying to remove something that couldn't be removed." Whatever that "something" was, the young physician knew he did not want to pass it on to his children. For as long as he could, he put off discussion of starting a family. When Linda finally prevailed but was unable to get pregnant, doctors discovered Rohr had no sperm. A moment of relief was followed by another realisation. He and Linda would adopt, and there would be still more reasons to never reveal his secret: Now he could lose his children as well as his wife. A solid and successful life For the most part, work took over Rohr's life. The family moved more than a few times: San Diego, Florida, Indiana, Massachusetts, Fort Bragg, his peripatetic pace less about overachievement than about trying to banish unwanted thoughts: "Hardly a day went by I didn't think about it."

When Boston Children's Hospital began its Gender Management Service in 2007, its clinic was the only one of its kind in the country. Today, there are more than 40 such clinics nationwide. The American Medicare system now covers hormone therapy and sex reassignment surgery for transgender people, and 15 states as well as the District of Columbia forbid insurance exclusions that discriminate on the basis of gender identity. While North Carolina recently blocked anti-discrimination protections for transgender people, 18 states and more than 200 cities and counties have laws prohibiting the abrogation of rights based on gender identity. Bill Rohr was in his 60s when the world tilted just enough for transgender issues to begin emerging from the darkness. Tall and slender, with a squarish face and fine white hair, the athletic youth had become a graceful older man. A respected surgeon, a loving husband and father, he'd built as solid and successful a life as a man could. Only once, in his 40s, did Rohr seriously consider giving up on being Bill and transitioning to Kathryn, or Kate, the name he called himself from an early age. But he just couldn't do it to his wife and kids. So he put the cork back in the bottle, as he liked to think of things, and there the cork stayed until the strangest sequence of events finally forced it out. A radical step

First, in 2002, were complications from a hernia surgery that sapped Rohr's energy and health. The subsequent testing showed he had virtually no testosterone in his body. The treatment, testosterone replacement, pushed him into hyper-drive mentally and physically. "He was wound up like a top, angry all the time," Linda said. "No patience, like he was going to explode at any minute." Rohr struggled on the male hormone for a number of years, but when he learned his extreme reaction could be evidence of his being transgender, he made a radical decision: He stopped taking it. He then took one more radical step. He began to self-medicate with female hormones, estrogen and progesterone, telling neither his doctor nor his wife. Almost immediately, Linda and others noticed a change. "He was suddenly so sensitive, so caring," she said. Indeed, for the first time in his life, Rohr felt truly happy and relaxed, which is "typical for a transgender person, once they get on the right hormones," according to Curtis Crane, a California surgeon who specialises in female-to-male gender reassignment.

Rohr started to grow his hair out, gathering his soft white strands into a ponytail so as not to draw too much attention. He also wore tight undershirts to help minimise his early breast development, which began initially as a side effect of the testosterone treatment. Things might have stayed that way if not for a small slip-up in early 2013. Linda, who worked as Bill's medical secretary, opened a package addressed to him and discovered a bottle of female hormones. He explained that the drug company must have made a mistake. The lie ate away at Rohr for two months, until one evening when the couple was having their weekly date night. They'd cooked dinner together and were relaxing with more champagne. That's when his wife of 44 years finally pressed him. "I want to know what's going on," she said. "What do you mean?" Rohr asked.

"You're not the same person. There's something going on, and I want to get to the bottom of it. How come you're so happy?" And that's all it really took. No more deceit, Rohr decided. Over the next several hours, he plunged in and unwound the secrets threaded through his life. Toward the end of the night, after the talking, crying and even laughing, Linda said: "I think we can work through this, but I don't know where we're going or what the rules are. I need time." "I will not only give you time," Bill replied, "but just like in the New York City subway, there's a red handle. You pull the red handle and everything stops." They talked more, together saw a therapist, and always the conversation came back to where it all started: They loved each other deeply, and they didn't want to lose that.

As Linda said: "It's not about the gender. It's about the soul." Two months later, they told their children - daughter Megan, who was then 34, and son Matt, 31. "I wasn't shocked," remembers Megan, a former psychotherapist who says she and her brother were raised to be open-minded. Matt took the news in much the same way, as he and his father sat in the parking lot of a Home Depot near his home in New Hampshire. "I care so much about my parents, it's not even a question," Matt said. "This is our new normal."

As for their public life, Bill and Linda decided that at least until he retired at the end of 2015, he would continue to be Bill with his colleagues, his patients, his neighbours and his friends. He would "announce" himself as Kate after he fully transitioned. There was just one more question Linda still needed to ask: Why was it so important to have the surgery? Being transgender, he replied, he'd lived his whole life thinking that at any moment he could lose everything. "Once you have the surgery, they can't take anything away from you anymore." The big day On February 17, Kate Rohr finally did what she'd wanted to do for a lifetime. She changed her body's external anatomy from male to female. It was only 5 per cent of the journey, she said, but it was a very important 5 per cent.

Matt had messaged both of his parents before dawn. "Good luck today, we'll be thinking of you! See you on the other side :)," he texted. Kate texted back: "Love you Matt. Thanks. Dad." It all would be a whirlwind. She'd arrived at the hospital in a black turtleneck and jeans. "How are you?" asked the woman checking her in.

"It's Christmas!," Kate exclaimed. By 2pm, the 25,579 days Kate had lived, anatomically, as Bill were finally over. "She's a girl," surgeon Marci Bowers announced when she came out of the operating room. Everything had gone smoothly, and her handiwork was top-notch, she declared. "She's gorgeous," Bowers said. "On a sliding scale of one to 10, she's an 11." Linda beamed, hugged the surgeon, then quickly texted Matt and Megan with the news.

In the late afternoon, the 70-year-old patient was finally wheeled out of recovery and up to her hospital room. Linda was waiting there, of course, relieved and excited. When the hospital gurney rolled over the threshold, she started to laugh. "She still has a smile on her face," Linda said. "Can you believe it?" "This was never supposed to happen," Kate said, fully awake, yet in her own state of wonder. "I was supposed to go to my grave with this." Sitting on the nightstand was a small bouquet of orchids and roses, her favourites. Linda had bought them at the hospital gift shop once she knew Kate had made it safely through surgery. "This was a big day, a really big day," Linda said to no one in particular.

With that, she smoothed her spouse's hair, stroked her arm, then leaned down for a kiss. Washington Post Follow FairfaxForeign on Twitter Follow Fairfax Foreign on Facebook