Caitlyn Jenner used to wear women's lingerie underneath her suits before her gender transition.
The 67-year-old former Olympian was previously known as Bruce but admitted that she struggled with her true identity, even as she travelled around the country giving her motivational speech, 'Finding the Champion Within', to others.
She writes in her upcoming autobiography 'The Secrets Of My Life': "They don't know that underneath the business suit I am wearing panties and a bra.
"That I am not Bruce Jenner but a woman I will come to call Caitlyn, who still has to be Bruce except for stolen moments where I can be my authentic self. The speech that I give is called 'Finding the Champion Within'. All bulls**t.
"They don't know that when I look into the mirror I see something entirely different, a body I loathe: a beard that is noticeable no matter how close the shave, a penis that is useless except for p***ing in the woods
"I have [also] stolen makeup...not only from [ex-wife] Kris but the rest of Kardashian-troop, because - trust me on this - there is more makeup per user in our home than any in history. I have bought makeup how-to-books. I keep the books, along with my small collection of clothing, in a small closet with a lock in back of my own closet."
Meanwhile, Caitlyn has also revealed that she broke down in tears when her son Brandon offered his support for her gender transition.
When the reality TV star decided to tell her 10 children and stepchildren that she was planning to transition, she started with Brandon, 35, her son with ex-wife Linda Thompson, and was overwhelmed by his support.
She told PEOPLE: "The first thing I said (when) I was thinking maybe I should transition was, 'I have to talk to all my kids'.
"And so I went through all 10 of them, one at a time, because I didn't want them ganging up on me!
"I started with my son Brandon, because he's like our little family Gandhi. He just has this great outlook on life and a very open mind. I figured he would be the easiest, so I sat down with him and his wife Leah and told them my whole story."
"At the end, good old Brandon goes, 'You know, Dad, I've always been really proud to be your son ... and proud of everything you've done in your life. But I've never been more proud of you than I am right now.'
"I cried. It was a really nice thing to say, and that really set the tone for (telling the rest of the family) and I started moving forward."