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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! 

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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."

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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. 

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