Rob Lowe Reveals 'The Outsiders' Costar Tom Cruise 'Completely Knocked Me Out' During Boxing Match in the '80s: He's a 'Beast'

Yikes! Rob Lowe revealed he was once left unconscious after a friendly brawl with The Outsiders costar Tom Cruise .

The Parks and Recreation alum explained during his Monday, July 15, appearance on "The Rich Eisen Show" podcast that the two of them would work out together and were "running bros" when they weren't on set filming the '80s flick.

Lowe, 60, noted there was always "so much testosterone" around, noting, "We’re 18-year-old guys stuck on location. So we would have headgear, and we’d have mouthpieces in, but we would legitimately spar."

"Cruise is so competitive that we used to box in the hallway of the hotel we were staying at during Outsiders ," Lowe said, admitting he willingly participated even though he was much skinnier than the dad-of-three , 62, whom he called "jacked" and a "beast" at the time.

During one particularly memorable fight, Lowe was able to get in a "real clean" shot at Cruise — who instantly reciprocated with twice the power.

"I rang his bell, and the next I knew, I woke up — I was coming to, on the floor. And he, like, completely knocked me out," the West Wing star shared. "His eyes just went black, but that’s the stuff we did. That’s what guys do. Like Fight Club ."

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Though Lowe may have been scrawny back in the day, the teen heartthrob has become known for his ageless looks and fitness regimen.

In a recent interview, the actor aired out his concerns over the popularity of quick fix drugs like Ozempic .

"I see people who are taking all the new weight loss drugs and that's great, and it's really changed their lives," he said. "But my concern always is, okay, now what? What’s the plan for the longevity of everything?"

"I never ever talk about diets, I talk about lifestyle," the father-of-two noted.

"I'm trying to be even more disciplined now as I'm older just because as you get older, you need to watch what you eat even more than when you were younger," Lowe continued of keeping up with healthy habits. "So I tried to cut sugar completely as my new year's resolution. And now I'm figuring, okay, that's not sustainable for me, but how do I really watch my sugar consumption?"

Though he's now in his 60s, Lowe, who's sober , insisted he currently feels "better than I’ve ever felt."