Robert Downey Jr. will join Zach Galifianakis in Todd Philips' "Due Date," Entertainment Weekly reported.
Robert will star as a dad-to-be who has to race across the country in time for his child's birth, with Zach playing what the mag called an "unlikely travel companion."
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The film will find Zach reuniting with Todd, who directed him in this summer's surprise hit "The Hangover" – which, with over $240 million in box office grosses, has become the highest-earning R-rated comedy in history.
"Due Date" could potentially start filming this fall with a summer 2010 release in mind.
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Robert just wrapped filming on "Iron Man 2," also due next summer, and stars in the upcoming "Sherlock Holmes" alongside Jude Law and Rachel McAdams.
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