‘Life isn’t fair,’ John Stamos reveals the ‘awful’ chapter of finding ex-girlfriend Teri Copley in bed with Tony Danza

In his new memoir, If You Would Have Told Me, John Stamos, 60, reveals a shocking episode from his past: he once caught his ex-girlfriend Teri Copley in bed with Tony Danza.

Stamos, who rose to fame as Uncle Jesse on Full House, writes that he was dating model actress Copley in the 1980s when he walked into her guesthouse and saw her sleeping with another man. The man had “ripped abs” and Stamos did not recognize him at first.

Stamos quoted to PEOPLE that the experience was “worse than anything” and “physically painful.”

“I can’t explain it, but I would’ve rather been punched in the nose again or something because the pain is so overwhelming,” he says, according to Entertainment Weekly.

“Looking back, it’s like, probably, she wasn’t the right girl for me. So seeing him, realizing it was him and stuff, it was hard. I mean, it was awful.”

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The 60-year-old actor says he ran out of the room “breathless” and with tears streaming down his face.

“At first I was like, ‘I’m going to kick his…’ I didn’t know it was [Danza] yet. I see his abs. I’m like, ‘Maybe not. F**k it.’ And I ran,” Stamos recalls.

“But I remember running down the driveway with tears streaming down my face and I didn’t want anyone to see me.”

Copley, now 62, denies that she cheated on Stamos, telling PEOPLE that they had already broken up when the incident happened.

“I wondered, ‘What was John doing there?’ because we had broken up,” she says. “He just looked at me and shook his head, and walked away.”

Stamos says he realized that the man was Danza, now 72, after he saw a poster of Copley in the front seat of a car parked outside her house. The poster had the inscription “My Dear Tony.”

“I jump in the El Co, start the car, and Elton John is still singing, and that’s when it hits me,” Stamos writes.

“I mouth the words to his most famous lyrics and realize the name of my rival: ‘Hold me closer, Tony Danza. . . .’”

“It took me a long time to get over that,” he tells PEOPLE.

The Big Shot star describes Copley as “just a nice person” but admits that he was “too immature” and “not a man” at the time.

“I mean, it wasn’t right to cheat on me, but I was too immature; I wasn’t a man,” he says.

“I didn’t become a man for a long time and I think she was… I don’t know. I was broken.”

Stamos says he decided to share the story in his memoir because he wanted to relate to his readers.

“I really wanted to find relatable things that happened in my life,” he cited.

“Because I think everybody thinks, like, ‘Oh, this guy’s got no problems. I’m sure he’s never been cheated on.’ ”

Stamos says that when people are cheated on, they “make a list” of reasons why they were left.

“It’s like, ‘Oh, she left me because I don’t have enough money,’ or ‘I’m not good-looking,’ or this and that.”

“And then you look at me and I go, ‘Well, he had all those things,’ ” he said. “People are s*****. And it’s life.”

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The actor also notes that there was a silver lining to the situation. He credits Danza’s popular show Who’s the Boss? with helping Full House succeed in its first season, as it aired right before it.

“Back then you go, ‘Life isn’t fair.’ And then, ‘Oh, wait a minute. It got evened out,’ ” Stamos told.

“I honestly believe if we didn’t follow his show in the summer, that would’ve been one and done for that show, Full House.”

Stamos adds, “That’s a big part of everything too, is sometimes the hardest thing to do is go with the flow. Because if you’re a good person, and you treat people well, and [lovingly], you do good things in the world, most of the time, you’re going to be okay.”