The interview, an ABC exclusive, began with an emotional Jenner who admitted how "being Bruce hasn't been an easy road."
"I've lived a lie my whole life," said the 65-year-old Olympic athlete who early in the interview took out his ponytail and let his long hair hang loose, "I can't do that anymore."
When asked by Sawyer if he's a woman, he answered, "Yes, for all intents and purposes, I am a woman."
The two-hour show, which included interviews with doctors, and experts as well as commentary from transgenders, focused on Jenner's history, starting with his Westchester upbringing (he was born in Mount Kisco, N.Y.).
Jenner and Sawyer traveled to the Sleepy Hollow apartment where Jenner grew up and where, at age 15, he first tried on women's clothes from his mother and sister's closets.
"At the time I didn't know why I was doing it," he said, "All I knew is that it made me feel good."
The reality show dad further explained that his 1976 Olympic win and fierce competitive drive was a direct reaction to tap down his female desires and prove his masculinity. He married (three times), had kids (he has six biological children plus the four Kardashian stepchildren) and admits he probably wasn't as honest with his wives as he could have been.
"I downplayed it," he said of his secret. "I probably didn’t say this was down deep in my soul."
The big surprise: Jenner had been on female hormones in the '80s for five years. It was a time, he said, that he finally felt like some of his demons were put at bay. But societal pressures and meeting Kris Kardashian Jenner around this time made him stop.
Of his marriage with Kris who caught him a few times in women's clothes (as did his other wives): "We tried to deal with it on our own," he said.
Eventually, however, as the Kardashian show got bigger and bigger, Jenner faded more and more into the background. "We had done 425 episodes over eight years and I kept thinking oh my god, the one real true story in the family is the one I was hiding and the one that could really make a difference in people's lives," he said.
As he reached his 60s, he knew he could no longer endure living someone else's life. "I realized, if I die, I'd be so mad at myself if I didn't explore this side of myself," he said.
He talked, too, about how difficult it was to tell his children and how challenging it's been being hounded by the paparazzi.
And, he admitted to suicidal thoughts. "I can see where people could get to that point and the pain would be over," he said "But I want to know how this story ends."
Jenner said he hopes his decision to tell his story will help other transgenders out there as well as the general public understand the community better.
"My whole life has prepared me for this," he said. The 20/20 interview was the last time he will be addressed as "he." The next time the public sees him, he will be "she."
"I will emerge as myself," he said, though he admits he's not ready for sexual reassignment surgery.
"I just want to have a free soul and enjoy life as who I am," he said. "It's that simple."
And for those who are still looking for more information, his documentary will air this summer and his oldest kids will be on ABC's "Good Morning America" April 27.
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