"I never thought I would get to kiss Michael Douglas," Damon, who will play the boyfriend of Douglas's Liberace, told PEOPLE Tuesday at the premiere of a different film, the documentary His Way, in Los Angeles.
"I kind of think of it in algebra terms, back to my high-school days," added Damon. "It's like the transitive property – by kissing Michael Douglas, I am making out with Catherine."
He's referring to Douglas's wife, Catherine Zeta-Jones.
"I was actually kind of upset that I never got to kiss Catherine," the father of four daughters deadpans, "but now I get to kiss Michael. I thought it would have been better if I could have at least kissed them both."
Source: People