Sylvester Stallone wound up in intensive care thanks to one punch from “Rocky IV” co-star Dolph Lundgren.

The “Rocky” headliner opened up about the animosity he held towards his co-star and how it ultimately landed Stallone in the hospital. “Dolph Lundgren walked in, and I hated him immediately,” Stallone said during a Q&A at Cannes Film Festival on Friday, per Vulture.

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“I had to find a superhuman being as an opponent, someone who would be overwhelming,” Stallone said of Rocky’s Soviet Union opponent. “Oh, that’s right, he’s perfect… This is what I would imagine they would create as an athlete — someone who is literally perfect. Indestructible. Shoulders, calves, forearms, giant butt, neck, back, everything.”

“I told him, ‘Why don’t we just do it? Just try to knock me out. Really cut loose as hard as you can.’ That was a really stupid thing to say,” Stallone confessed. “Next thing I know, I’m on a low-altitude plane to the emergency room, and I’m in intensive care for four days. And there are all these nuns around.”

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The punch had such an impact it very nearly killed the actor. “He hit me so hard he almost stopped my heart,” Stallone said.

Stallone and Lundgren ultimately made amends, reuniting for all three “Expendables” movies and the upcoming fourth film.