The 'RHOBH' alum made the shocking revelation during an appearance on Jeff Lewis' radio show Tuesday.
During an appearance on SiriusXM’s Jeff Lewis Live Tuesday, Mellencamp, who was joined by her Two Ts in a Pod co-host, revealed that she had a one-night stand with Matt Damon when she was just 20 years old.
"She mentioned it on a podcast, and then went back and told producers, 'Take that guy's name out,'" Judge told Lewis. "And so now, I tell people, 'If you guys wanna know, just DM and I'll tell you who it is.'"
"She tells people on the DMs. I'm like, 'Stop telling people," Mellencamp exclaimed. "I did not want to out this guy. Who knows?!"
Mellencamp, who has since married Edwin Arroyave and welcomed four children with her husband, was just 20 years old when she said she used a fake ID to get into a club where she reportedly met the Air actor.
"He was probably 30 -- ten years older," the 41-year-old reality TV star surmised. "I only slept with him one night. He didn't get my number."
She continued to push back on revealing who the A-lister in question was, though Mellencamp offered several hints, including "He has a very famous best friend as well."
Damon's name was eventually guessed by one of Lewis' producers, to Mellencamp's shock and surprise -- and Judge's pokes and prods.
"You guys! There's so many other MDs out there. There's Matt Dillon," Mellencamp said. "There's Michael Douglas."
Lewis was equally surprised by the news, but thrilled nonetheless, telling The Real Housewives of Beverly Hills alum, "Wow. Congratulations, Teddi."
Damon, meanwhile, has been married to his wife, Luciana Bozán Barroso, since 2005. The pair share daughters Isabella, 16, Gia, 14, and Stella, 12. Damon is also the stepfather of Barroso’s 24-year-old daughter Alexia, whom she shares with ex-husband Arbello Barroso.
While the Oscar winner has never addressed his alleged hookup with Mellencamp, his previous dating history has a few celebrity names attached, including Winona Ryder, Claire Danes and his Good Will Hunting co-star, Minnie Driver.