Grint plays a drug-addled traveler in the movie, set in Bucharest, which screened at the festival Saturday. One of 19 competing for the event's Golden Bear award, it centers on an improbable romance between an American traveler played by LaBeouf and a troubled Romanian musician, played by Evan Rachel Wood.
Grint played Harry's faithful friend Ron in the Potter films.
He told reporters: "After playing the same character for 11 years, it's nice to do something completely different." He added: "The character was someone who's completely the opposite of Ron."
Take ABC13 with you!
Download our free apps for iPhone, iPad, Android and Blackberry devices