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Jodi Guglielmi
May 03, 2017 05:25 PM

Naomi Watts and Liev Schreiber know how to keep things professional.

The former couple costar as husband and wife in the upcoming boxing film Chuck, despite ending their 11-year relationship.

But Chuck Wepner, the real-life heavyweight boxer on which the film is based, tells PEOPLE the exes were able to put their personal lives aside while on set.

“They had split up and separated before the movie even started but they came on the movie and they acted just like they were married,” he says. “They were friendly.”

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Wepner says he is grateful that Watts and Schrieber waited until after filming wrapped to announce their split.

“They didn’t want to do anything to screw the movie up, which I thought was absolutely wonderful,” he says.

RELATED VIDEO: Naomi Watts and Liev Schreiber Split After 11 Years Together

The former couple announced the end of their relationship in a joint statement to PEOPLE in late September. They share two children.

“We’re parents together so we’ll be together for the rest of our lives no matter what and we’re very close,” Schreiber previously said of their split. “Hopefully, that never changes and I don’t think it will.”

Chuck, a ’60s-set biopic, stars Schreiber as the famed heavyweight boxer. Watts plays his wife, Linda. 

The film hits theaters on Friday.

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