Sean Penn says Matt Damon calling him 'a stupid schmuck' convinced him to star opposite his daughter in a new movie

• Sean Penn and Dylan Penn star as a father-daughter duo in "Flag Day."
• Penn said Matt Damon called him up before they started shooting to persuade Penn to take the role.
• "That was the last straw. Once I decided to do that, it was a big burden off me," Penn said.

Sean Penn said his decision to star in his daughter's debut film was influenced by Oscar winner Matt Damon.

"Flag Day" premiered at the Cannes Film Festival over the weekend and stars Penn and his daughter, Dylan, as a father and a daughter, who's struggling to make amends with her fractured family.

Penn was already directing the family drama film, but had never before acted in a film he had directed. Indiewire reported that during the press conference after the film's premiere, Penn explained that Damon persuaded him to be in the film.

"A month and a half before shooting started, Matt Damon called me, not to say he could or couldn't, but that I was a stupid schmuck not to take this opportunity to act with my daughter in this thing," Penn said.

"That was the last straw. Once I decided to do that, it was a big burden off me."

The elder Penn was not the only person who had doubts about starring in the film.

At the press conference, Dylan said: "I was apprehensive before I said 'yes.' I first read it when I was 15 and came back to it when I was 30. I could reference my own experiences and bring something to this character."

"Flag Day" is based on a memoir, "Flim-Flam Man: A True Family History," written by Jennifer Vogel about her father's double life as a con man and bank robber. In the film, Dylan plays Vogel while Penn plays her father, John Vogel.

Penn said when he read the book, he saw his own daughter's face.

"In a film about deception, about the search for truthfulness, it goes back to Dylan's face," he said. "I find her uncontrived."

He added: "When you can put a camera on an actor listening, that tells the whole world of truth and deception. My cinematic focus was on Dylan's face to tell the story."

The producer William Horberg and Jon Kilik had tried more than once to persuade Penn to take the role as John Vogel before Damon's intervention.

"As a producer, you dream," Horberg told the conference. "When I dreamed from the beginning to make the movie with Sean Penn as John Vogel, to have a real father and daughter play a father and daughter, knowing Sean's commitment to authenticity, this was a special way for this story to be told.

"We didn't compromise. We had to fight hard to get the resources, to get Sean to do this."