"For all intents and purposes, I am a woman," he said. "People look at me differently. They see this macho male, but this female side is part of me, it's who I am. I was not genetically born that way."
The former Olympic decathlete touched on a wide variety of topics, from why he wants to be transgender to what he'd like to be called by his children.
"I'm actually really excited about the future," Jenner said. "I'm actually, for the first time in my life, looking forward to the future."
Jenner, who said he wanted to be referred to as a "he," did not give any indication what name he might adopt as a woman.
Jenner's interview with Sawyer was highly anticipated by fans and the tabloid media, which had previously speculated that the television personality identified himself as female.
Jenner said he began his gender transformation from male to female in the 1980s when he began hormone replacement therapy, although he recognized when he was very young that he enjoyed wearing women's clothes. However, he said, he does not believe himself to be gay.
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"You understand that people are baffled, confounded. Are you gay?" Sawyer asked.
"No, I'm not gay. I'm not gay. I am, as far as I know, heterosexual," Jenner replied. "I have never been with a guy. I have been married, raising kids."
Sawyer then expressed the confusion that being a transgender female who is attracted to women might create.
"You are going back to the sex thing, and it's apples and oranges," Jenner said.
The 1976 Olympic gold medalist appeared during the interview with long, dark hair and told Sawyer has is taking female hormones -- a method chosen by many transgender people as part of their transformation. Another method is sex reassignment surgery -- something that Jenner said he might do someday.
"Those things are all things that are out in the future for me to explore," Jenner said.
During the "20/20" interview, Jenner showed Sawyer a closet full of women's clothing and told her that he plans to change his identity on his driver's license from male to female.
Regarding how Jenner would like to be addressed by his children, he said that conversation has already occurred.
"I asked him, you know, 'What do you want us to call you?'" Jenner's oldest daughter, Cassandra Marino, said. "And he just interrupted me and just said, 'I'm Dad. You know, you can call me dad... I will always be your dad.' And that was just a huge relief."
Jenner has two biological children and four stepchildren with ex-wife Kris Kardashian, with whom he was married between 1991 and 2014. When asked if he might remarry someday, Jenner said that might be a tricky question to figure out.
"I can't even figure that side of it out. I just want to have a free soul, and have a lot of great friends," Jenner said. "I'm going to learn a lot in the next year ... 2015 is going to be quite a ride."
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