Film stars Kevin Costner and Ashton Kutcher walked the red carpet in Berlin on Sunday (October 1) as they attended the premiere of their new film "The Guardian". The action drama sees Costner and Kutcher star as members of the American coast guard unit. A troubled young man, played by Ashton Kutcher enrols in the coast guard, hoping to find meaning in his life. During the demanding and physical coast guard training, Kutcher's character is taken in by a veteran rescue team leader, played by Costner. Kutcher, known to television viewers for his hidden camera show "Punk'd" where he and a team of pranksters play tricks on celebrities, said he hadn't yet "punk'd" on his co-star Kevin Costner. Kutcher said it would have been too dangerous to play a prank during filming of "The Guardian", but admitted he'd consider trying to "punk" Costner in the future: "I couldn't on the movie because there was too much stuff that we were doing that was too dangerous and if he was like hanging from a high wire and gonna die and he was like 'are you punking me, are you trying to punk me' that wouldn't have been a good thing so I kind of had to refrain thus far," he said. Signing autographs on the red carpet accompanied by his wife, Christine Baumgartner, Costner said that although he was aware of Kutcher's reputation as a trickster, both actors had taken their roles seriously and didn't joke around during the filming of the action-packed film. "He's a real professional and we had an agreement that we wouldn't do that [play tricks] because there was too much on the line for us to ever guess if it was a joke or if it was something real," Costner said. "The Guardian" opens in cinemas across Germany on October