When Sean Penn first read the script for “Flag Day,” he knew his daughter Dylan needed to play the starring role.

“Rarely have I ever had an actor’s face dominate what I was reading on the first read of the script, and Dylan’s face was imprinted on it by page 30,” Sean told Variety at the film’s premiere on Wednesday at the Director’s Guild of America in West Hollywood.

The movie, also directed by Sean, marks the first time Dylan has starred alongside her father.

“The intensity was what I expected,” Dylan said. “But the playfulness of working with him as a director and as a co-star was really surprising and a relief at the same time. Playing off of him as another actor is really easy because he gives you a lot to work with.”

While “Flag Day” tells the true story of Jennifer Vogel and her counterfeiting, bank-robbing father John Vogel, both Penns said they were able to infuse parts of their own father-daughter relationship into the film.

“We have parallels in the humor of their dynamic and in the flaws — in particular, myself as a father,” Sean said. “In the end, what was the most common was that I love my kids until the end of the earth, and I believe that John Vogel did too in his own messed up way.”

Co-star Katheryn Winnick, who plays Patty Vogel, said one reason she was drawn to the movie — which also stars Sean’s son Hopper Jack Penn — was the prospect of working with the Penns.

“It’s a Penn family movie!” she said. “And I got to be part of that family. We had movie nights, we had game nights, we had dinners.”

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Katheryn Winnick Eric Charbonneau

Both Sean and Winnick expressed a desire for audiences to (safely) see the movie, which was shot on 16mm, in theaters.

“I’m so grateful to MGM for giving this a period of time to allow audiences to see it exclusively theatrically before it goes into tiny phones,” Sean said in front of the premiere’s fully vaccinated audience.

Sean, who made headlines recently for stepping away from his Watergate drama series “Gaslit” until all cast and crew get vaccinated, said he has not yet returned to set.

“I will return once they resolve it,” he said. “We’re still looking for some stronger leadership within some of the unions to get to the point where all exercise common sense and recognize that without interdependence, there is no independence. And this is a call for all to honor interdependence and get vaccinated.”