The Keeping Up With the Kardashians star claimed she and her older sister Kendall Jenner, 20, always had suspicions about Bruce after discovering their father wearing women's clothes when they were much younger, though they never talked about it.
She said: "And I've honestly known about it for a really long time and we actually caught him then dressing up as a girl. When my sister and I were like six and seven maybe. So we've known for a while that there was something, but it was never talked about.
"Honestly, like I'd be with my girlfriends sometimes and he would come in and be like what are you guys talking about and kind of joke around and I knew there was something, but now I feel like we hang out a lot more there's no secrets.
Now Kylie is hopeful her acceptance of the I Am Cait star will help inspire other young people.
More from Spy:
• Police search du Plessis-Allan's house
• Insta-wrap: In-jokes and pyjamas
Speaking in an interview on the Ellen DeGeneres Show, she said: "She's really living her authentic true self. And I feel like that's awesome and also I want to be someone from my generation to like be an example because I think that's so awesome.
"I think that other girls and boys my age will maybe see that I'm so accepting and be accepting of other people too."
-Bang! Showbiz