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Friendly exes!

Maria Shriver and Arnold Schwarzenegger separated in May, but that doesn't mean they didn't spend the holidays together! 

A source tells Us Weekly that Schwarzenegger, 64, and Shriver, 56, attended Saturday's Christmas eve mass together. "They were serious but seemed like one family unit," says a source. "The kids were between them most of the time, but Arnold and Maria definitely seemed civil and would talk once in a while. They hugged the pastor at the end of the service and seemed warm and happy."

So why did the duo split after 25 years of marriage? Schwarzenegger secretly fathered a son, Joseph, now 13, with Mildred Baena, the family's housekeeper for over 20 years. "I have so much love and respect for Maria," Baena later said. 

Schwarzenegger and Shriver are parents to Katherine, 22, Christina, 20, Patrick, 18, and Christopher, 14.