Robert Downey Jr's first meeting with Zach Galifianakis didn't go to well as he mistook him for a crazed fan.
The Iron Man 2 actor is set to star alongside Galifianakis in comedy Due Date next month but Downey Jr thought he was going to have to punch him when they first met.
Speaking to Showbiz Spy the actor said: "Before we started shooting I was down in Venice and some weird guy walks by and goes, 'Hi, I think I'm doing a movie with you and [director] Todd Phillips'.
"I thought, 'I might have to punch this guy'. And then I realised, 'Oh my God, that's Zach'. We have definitely come a long way since then."
Due Date is the first film for director Todd Phillips since the huge success of The Hangover last summer, a movie which reunites him with Galifianakis.
It's the second film of the year for Downey Jr after the success of Iron Man 2 at the box office this summer. The actor is currently filming a second Sherlock Holmes movie and is set to reprise the role of tony Start in The Avengers.
Due Date is released 5th November.
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