ET caught up with Kris at Cosmopolitan's 50th anniversary celebration in West Hollywood, California, where she was joined by daughters Kim Kardashian, Kourtney Kardashian, Khloe Kardashian and Kylie Jenner.
The ladies, plus Kendall Jenner, were featured on the cover of Cosmo's 50th anniversary issue, on newsstands Tuesday.
Inside the pages of the magazine, Cosmopolitan digs beneath the surface of the family to get the stories that fans have never heard.
"The most embarrassing moment for me was when I was with [Caitlyn (formerly Bruce)] on a commercial airliner in first class. We joined the mile-high club and we felt we got away with it," Kris says in a behind-the-scenes clip of the photo shoot. "We had sex in the bathroom and we came out and nobody said anything. At the end of the flight, the flight attendant got on the microphone. 'Congratulations, Mr. and Mrs. Jenner! You've just joined the mile-high club. We're so proud of you, and we decided to give you a bottle of champagne! Yay!' I could not squish down in my seat low enough. I was mortified."