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.”
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.
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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.”
The film hits theaters on Friday.