Hilary Duff and Mike Comrie are definitely friendly exes.

Despite Hilary officially filing for divorce last month after a year of being separated from her former NHL player husband, the two came together to throw a birthday party over the weekend for their son Luca, who turned three years old last Friday.

Hilary's big sister Haylie took to Instagram to document the fun.

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"Going hard for Luca's 3rd birthday," she wrote alongside this snap of her and the 27-year-old "Younger" star indulging in a cupcake.

Haylie later proved she's still tight with her sister's 34-year-old ex by posting this heartwarming picture of Comrie carrying Luca's huge birthday cake made out of mini cupcakes with the help of her own fiancé, Matt Rosenberg. In December, Haylie announced that she and Rosenberg are expecting their first child together.

"Cutest Dad-to-be & Dad around! @mattyrose3 & Mikey," she captioned the pic.

Cutest Dad-to-be & Dad around! @mattyrose3 & Mikey ��

A photo posted by haylieduff (@haylieduff) on

Earlier this month, Hilary told Cosmopolitan magazine that she has no regrets when it comes to her marriage with Comrie.

"Mike and I were very in love when we met," she said. "We both really wanted to get married. I'd been working since the age of 11 or 12, so making that choice at a young age seemed right for me. Maybe it wasn't, but we spent the majority of our time together really happy."

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"It wasn't working well enough to stay together, but there was still a lot of love involved," she added. "It was just a slow set-in of us not being the match that we used to be. I'm lucky for the person he is and I am, and how we decided to handle this."

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