Most people are already aware that CNN anchor Anderson Cooper's mother is famed socialite Gloria Vanderbilt, but not even Cooper was aware of how many famous men she had hooked up with until he started watching old movies with her.
Cooper appeared on "Late Show With David Letterman" on Wednesday and got to chatting about his now 90-year-old mom's romantic dalliances back in her day.
It all started with an innocent question about whether she'd known Marlon Brando.
"It turns out my mom and Carol Matthau, who became Walter Matthau's wife ... they both saw 'On the Waterfront' together and they both decided they wanted to hook up with ... Brando," Cooper said to an amazed Letterman.
"So Carol was the first one to do it and then she set it up for my mom!"
"This is remarkable," Letterman said, clearly impressed.
"When she was 16 or 17, she went to Hollywood to stay with her mom," Cooper continued. "And her mom was not exactly a hands-on parent. And my mom was out hooking up with Clark Gable ... Errol Flynn.... Watching old movies with my mom is a trip."
Not to be outdone, Letterman offered up a shocking romantic secret from his own mom's past. Who was it? And do we actually believe it to be true?
It doesn't really matter. Just the thought of it is enough to creep Letterman out for hours.