"My mom knew," the reality star told Vogue magazine in their iconic September issue. "She knew since their third date."
Kris Jenner said in an episode of "I Am Cait" that she wasn't told about her husband's transition "early on." Kris and Caitlyn were married for 23 years before splitting last year.
Still, Kendall Jenner, a model, said she had known for years, even accidentally seeing Caitlyn once.
"But my whole life we would, like, catch her, and we would be like, 'What is going on here? I think we know, but do we?’" Kendall, 20, recalled. "And then one time I actually ran into her. In this house. She had no idea.
"She would wake up really early just so she could dress up and move around the house and get that little kick for the morning, and then go back to being Bruce; take us to school, totally normal," she continued. "So one morning I woke up at 4:00 a.m. so thirsty, came downstairs into the kitchen, and grabbed a bottle of water. And as I was coming back out, my dad was coming down the stairs in, like, a wig and makeup and shoes; the full nine. And she didn’t see me."
Kendall then added that she "literally froze," hoping that her dad would "turn right" so that she wouldn't catch her.
"Thank God, she turned right and -- to this day -- has no idea that happened," she added. "That was the first time I had ever seen her."
In the wide-ranging Vogue interview, Kendall also spoke about how she's "superdifferent" than her "Kardashian sisters," referencing older sisters Kourtney, Kim and Khloe.
They're Kris Jenner’s children from her marriage to Robert Kardashian, which ended in 1991 before the famed attorney died 12 years later.
"They’ve always been into the glam thing and dressing up every day and being in the thick of it. Part of me loves that, but at the same time, I love dressing down and having my private life," she said. "It’s almost, like, empowering to know that no one knows we’re sitting here right now, because it’s not usually like this."
Besides Kendall, Kris and Caitlyn Jenner had another child, Kylie, together.
Kendall said she takes her privacy seriously, even borrowing cars from friends and family to throw off the ever-present paparazzi.
"Sometimes, it takes me an hour to figure out how to get rid of these guys who have been following me all day,” she said. “And the second that I feel it getting the better of me, I have to go chill myself out, go take a bath or something to, like, disconnect from it. It keeps you real and sane and humble.”