Kris Jenner Says Her Most Embarrassing Moment With Caitlyn Jenner Was Joining Mile-High Club

When you're a Kardashian, there's no such thing as oversharing.

When you're a Kardashian or a Jenner, there's no such thing as oversharing.

Matriarch Kris Jenner was joined by all her daughters -- Kim Kardashian, Khloe Kardashian, Kourtney Kardashian, and Kendall and Kylie Jenner -- for the cover of Cosmopolitan's 50th anniversary issue, hitting newsstands Oct. 13.

WATCH: Khloe Kardashian Rocks Booty-Baring Swimsuit While Demonstrating Lunges

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. "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."

It's no secret this clan has some outrageous stories, but it's the headline on Cosmopolitan's cover that's putting subscribers in an uproar. The title dubs them "America's First Family," causing some readers to threaten to cancel their subscriptions. Cosmopolitan editor-in-chief Joanna Coles explains the move to ET.

WATCH: Kris Jenner Thinks Jail Could Be the 'Biggest Wake-up Call' for Scott Disick

"We were being tongue-in-cheek and an enormous controversy has come from this," Coles says. "We have also heard from within the White House. I am reliably informed that the actual first family is amused by this and have no intention on giving up their bedrooms in the White House for the Kardashians."

Caitlyn Jenner is the only female member of the family not included in the cover photo, which was reportedly the first time that the group of ladies was in the same studio together since 2011.

WATCH: Caitlyn Jenner Stuns in Red Pantsuit and Lacy Bra

The magazine dedicates 16 pages to the reality family, who couldn't have been happier with the results.

"Happy 50th birthday @cosmopolitan!!!" Kris posted on Instagram. "So honored to be on the November cover with my girls!!"