In fact, Sylvester admits that the duo actually really hated each other amid their box office rivalry in the 1980s and 1990s.
"We couldn’t stand to be in the same galaxy together for a while. We truly, truly loathed each other," Sylvester said on a recent episode of The Jonathan Ross Show.
So, while Sylvester was starring in flicks like Cobra and Tango & Cash and Arnold was making headlines for Conan the Barbarian and The Terminator, the pair let their competitive instincts get the best of them.
"This may sound a little vain, but I think we were pioneering a kind of genre at that time, and it hasn’t been seen since really," Sylvester explained to Forbes.
He continued, "So, the competition, because it’s his nature, he is very competitive, and so am I…and I just thought it actually helped, but off-screen, we were still competitive, and that was not a healthy thing at all."
Since then, he says he's "become really good friends" with Arnold, and they've even shared the screen in films like The Expendables and Escape Plan.
Although it was a rocky road to their friendship, it sounds like these two realized it was more effective to team up than be bitter rivals!