Arnie: I used to hate Stallone
The Terminator star is now friends with the Rocky actor, but confessed that the perceived rivalry between them when they were the big action stars of the 80s was real, reported Digital Spy.
Speaking at a Q & A session in London, he said: "I hated the son of a b***h!
"When I saw Rambo II, I saw Sly with his clothes off and he looked totally ripped. I said, 'What the f*** is he doing in my department? In the Rocky movies, he was athletic and smooth but he wasn't that ripped. Does he have less body fat than I have? I have to get him. If he thinks he's stepping into my territory, I'm stepping into his and outdo him in the movies.' This is where the battle began.
"He was like a competitor that I had to go and destroy. We were competing on who had less body fat, who was killing more people on-screen, who was killing people in the most unique way, who had the biggest box office, who has better reviews. It was an all-out battle for a decade. People asked me, 'What do you think of Sly's movies?' I'd say, 'They're s**t!'."
However, the actor - who is returning to one of his best known roles in the upcoming Terminator: Genisys - said he and Sly have " become very good friends since then".
He added: "And even in the time I didn't like him, I admired him obviously. He's a great writer, director and actor."
The pair also teamed up for Sly's Expendables franchise.
Arnie, 67, also hinted that there could be a follow-up to his 1987 sci-fi film The Running Man.
He told the audience at the event: "There's rumblings of a new Running Man movie, so it's a great honour to be asked back."