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Robert Downey Jr has admitted he wasn't sure who his co-star Zach Galifianakis was when they first met.
The pair star in Todd Phillips' latest movie Due Date, about a businessman who is forced into a road trip with an aspiring actor so he can get home for his child's birth.
Discussing how Zach approached him on the street to reveal they were working on a movie together, Rob confessed: "Susan my wife was there and was worried for me. I tend not to recognise people. I didn't know exactly who Zach was yet."
He joked: "I looked like I was going to drop him on the pavement. I don't like punching Zach, but it has to be done."
Zach added: "He doesn't punch me. He pinches me, and it drives me absolutely insane."
Meanwhile, Zach, who also starred in The Hangover, said the secret behind their on-screen chemistry is "insults, insults, insults".
The film had its London premiere in Leicester Square on Wednesday night.
