Patrick Dempsey has joined the cast of Transformers 3.
According to Paramount Pictures the actor is the boss of Mikaela Banes, the returning Megan Fox, and is going to be important in the movie's plot.
Transformers 3 will be the first big budget blockbuster movie for the actor, who made his name in hit U.S. medical drama Grey's Anatomy.
He told Brazilian website BOL: "I start filming later this month. In 'Transformers 3' I play a character who is far more dark than others I've played."
Shia LaBeouf is back as Sam Witwicky while Michael Bay is once again in the director's chair as filming gets underway this month.
Transformer: Revenge of the Fallen was released last year and, despite poor reviews, the movie went on to gross over $836 million at the global box office.
It out grossed it's predecessor Transformers, which was released back in 2007, which took $709 million when it was released.
Transformers 3 is expected to hit cinemas in 2011.
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