Deny, deny, deny. That’s the way Kris Jenner has dealt with Caitlyn Jenner’s claims that she knew all about her then-husband’s struggle with gender identity when they married in 1991. But now the story she so carefully cultivated has been torpedoed — by her own daughter Kendall Jenner! “My mom knew,” the supermodel spills in the new issue of Vogue. “She knew since their third date.” It was a bombshell statement. Kris, 60, has repeatedly sworn that she was blindsided when the former Olympian, 66, publicly revealed that he wanted to be a woman, while Caitlyn insists she was open about it with Kris. While Kris admits that Bruce once confessed he’d taken hormones in the ’80s, she claims he never told her why. She also says she knew “that…