John Stamos shares shocking details about her former girlfriend’s cheating…

John Stamos alleges he discovered his ex-girlfriend in bed with Tony Danza.

Stamos, 60, alleges in his new biography, If You Would Have Told Me, that he walked in on girlfriend Teri Copley in bed with Danza, now 72, while they were dating in the 1980s.

According to the Full House alum, the experience was “physically painful” and “worse than anything.”

“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 said. “In retrospect, she was probably not the right girl for me.” So seeing him, recognizing it was him, and all that was difficult. I mean, it was terrible.”

Stamos claims he stepped into Copley’s guesthouse and discovered the actress asleep in bed with an unknown male with “ripped abs.”

Stamos claims he staggered out of the room backward after being “breathless” by the sight.

“At first, I thought, ‘I’m going to kick his…'” I hadn’t realized it was [Danza] yet. I can see his abs. ‘Maybe not,’ I say. F— it.’ “And I ran,” Stamos remembers. “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, claims her relationship with Stamos was already gone when the event occurred. “I wondered, ‘What was John doing there?’ because we had broken up,” she says to PEOPLE. “He just looked at me, shook his head, and walked away.”

In his biography, Stamos claims that he first recognized Danza after seeing a poster of Copley inscribed “My Dear Tony” in the front seat of an unidentified automobile parked outside of her house.

“I jump in the El Co, start the car, and Elton John is still singing, and that’s when it hits me,” Stamos says in his memoir, according to Entertainment Weekly. “I mouth the words to his most famous lyrics and realize the name of my rival: ‘Hold me closer, Tony Danza. . . .'”

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

Stamos describes Copley as being “just a nice person.”

“I mean, it wasn’t right to cheat on me, but I was too immature; I wasn’t a man,” he told PEOPLE. “It took me a long time to become a man, and I believe she was… I’m not sure. “I was shattered.”

Stamos claims that he included the claimed occurrence in his biography because it was relatable to him.

“I really wanted to find relatable things that happened in my life,” he said. “Because I think everyone thinks, ‘Oh, this guy’s got no problems.'” I’m sure he’s never been dumped.”

When people are cheated on, they “make a list,” according to Stamos. “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 jerks. And that is life.”

The actor also mentions that, in his opinion, everything “evened out” in the end. Stamos attributes this to Danza’s famous sitcom, Who’s the Boss? As the show’s lead-in, it was responsible for much of Full House’s early popularity. Full House served as a springboard for Stamos’ career.

“You used to say, ‘Life isn’t fair.’ Then he says, ‘Wait a minute.’ It evened out,’ says Stamos to PEOPLE. “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.”

“That’s a big part of everything, too,” Stamos continues, “because sometimes the hardest thing to do is go with the flow.” Because if you’re a nice person who treats others well and [lovingly] does good things in the world, you’ll be fine most of the time.”