“X-Men” stud Michael Fassbender admits that when his “12 Years a Slave” co-star Lupita Nyong’o won her Oscar this year, he had sneaked away from his seat.

“I was taking a piss,” he admits of his awards faux pas in a conversation with James McAvoy in the new issue of Details. “And I did have a sneaky vodka tonic. But I got totally caught out … I was thinking that category was going to be way down the line. And then, of course, you can’t get back in until it’s a commercial break, so I watched it backstage.”