Jimmy Kimmel’s “feud” with actor Matt Damon has been one of the longest-running gags on Jimmy Kimmel Live throughout its almost two-decade run. Kimmel has a habit of finishing the show by announcing that they had to truncate Damon’s appearance due to time constraints.

Various pieces on the show have even included Kimmel and Damon pretending to despise one another, including one last year when Kimmel said he was taking a break, and Damon interrupted, saying that he’d been hiding out in Kimmel’s house for three months. Now Damon is spilling the beans on how the fun rivalry began, and it turns out it wasn’t intentional.

“The Jess Cagle Show” presenter Cagle asked Damon, 50, how he first heard Kimmel close his late-night show with, “Sorry, Matt Damon, we ran out of time,” during Tuesday’s broadcast of Sirius XM’s “The Jess Cagle Show.”

“People started to call me and ask like, ‘Hey, what’s your connection to this guy?’ And I’d never met Jimmy,’” Damon stated. “He literally pulled my name out of thin air one night.”

“And the way he told me this story, he said he had like a, he said ‘I had a ventriloquist and a guy in a gorilla suit as my guests. And I just said kind of as a throw away, my apologies to Matt Damon when we ran out of time,’ but he could have said Brad Pitt,” Damon explained.

“He could’ve said, you know, George [Clooney] ― he could have said somebody else,” the actor said. “But he just, for some reason, maybe I had a movie out that week or something, but he just said my name. And it changed the course of both of our lives. We’ve kept this a feud going for, you know, it’s gotta be 15 years now. I’ve had a lot of fun doing it.”

Kimmel remarked the running gag “doesn’t behave like any joke ever,” according to Damon.

“He goes, ‘I say the same joke every night … and it gets a laugh every night,'” Damon explained.

“He goes, ‘It’s the weirdest thing.'”

Kimmel, 53, has previously addressed the genesis of the long-running joke. The late-night presenter stated Damon’s name “was just the first name that popped into [his] head” and his producer “got a kick out of it” so he “just started doing it every night to amuse him” in a 2013 interview with NPR.

“Matt Damon was just the first name that popped into my head,” the comic explained. “I was trying to think of an A-list star, and somebody we absolutely would not bump if he was on the show.”

Kimmel continued repeating the joke because it was doing well.

“The legs on this bit are unbelievable to me. I mean, people laugh every time I say it,” he told NPR. “Repeating the same joke every single night, you’d think eventually people would get tired of it, but they don’t.”