Robert Downey Jr has revealed that he has never worked with anyone like Zach Galifianakis.
The pair team up for Todd Phillips' new comedy Due Date, Galifianakis worked with Phillips on last year's huge hit The Hangover.
Downey Jr is forced to accept a ride home from wannabe actor Galifianakis as he tries to make it home for the birth of his child.
"I've never worked with anyone like ZG, because there's no telling what he might do.
"Just because you're on set doesn't mean that's where the scene's going to go, which to me is even a step beyond my own managed insanity.
"But it's not because he's not contained. He's just completely free."
"No one is really the straight man in this movie," added Downey, "but I am kind of like this stick that's pounded into the ground, that I think a lot of people can relate to."
But before Due Date Downey Jr is back as Iron Man in May, the second movie in the franchise.
Tagged in Robert Downey Jr Zach Galifianakis