Dermot Mulroney divorcing Prima Apollinaare after 15 years

Dermot Mulroney and Prima Apollinaare are ending their marriage after a decade and a half.

The Chicago Fire star signed a petition for divorce from Apollinaare on Saturday, according to court documents reviewed by Entertainment Weekly.

Mulroney, who appears to be representing himself, cited irreconcilable differences as the reason for the split and listed their date of separation as “TBD.” He is seeking joint physical and legal custody of the couple’s two daughters, Mabel, 17, and Sally, 15.

Per the documents, the actor is also requesting spousal or domestic partner support payable to himself, and requesting the termination of the court’s ability to award support to Apollinaare, who is a singer-songwriter.

A source with knowledge of the situation tells EW, “No one is asking for anything, and no one is denying anything. They are not arguing over the children nor money. They used mediators, not lawyers, as they are friends and this is amicable. They were advised to file this way which seems to have caused media confusion.”

Mulroney and Apollinaare started dating in 2008 and welcomed their first daughter later that year, according to PEOPLE. Their second daughter arrived in 2009, and the couple tied the knot in December 2010.

Last year, ahead of the release of Apollinaare’s fourth album, she and Mulroney opened up about their relationship and shared love of music after appearing together on the singing game show We Are Family.

“It was such an amazing phone call to get that the show reached out to us,” Mulroney told EW at the time. “They knew Prima’s music and put together that we are this sort of secret couple even though we’ve been together for 20 years. Kind of a stealth Hollywood couple. So it really works perfectly for this show. And then it was such an honor to be on a game show that helps other people and isn’t just fun and games, although we could not have had more fun.”

Apollinaare agreed, adding that the show was “fun” for her because of their musical backgrounds (Mulroney is an accomplished cellist in addition to being an actor). “We both like to do karaoke together and we both like music so much,” she said. “It was actually, for me, it was really an amazing experience to be on television and singing. Of course with my husband, I play with him all the time in the house. We all play instruments. We have harps, guitars, ukulele, pianos, you name it.”

She continued, “So we’re all musicians, but to actually do it and just have [contestants] winning money is also very rewarding. I’ve been singing since I was very little and music is my heart. So it was a great experience. They made it so easy for us. We had so much fun. I wish we could do it again.”

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This was the second marriage for Mulroney. The Anyone But You star previously wed actress Catherine Keener in 1990. The two, who share one son, separated in May 2005, and he filed for divorce in 2007.