Hilary Duff unites with ex Mike Comrie to celebrate son Luca's 4th birthday

Chloe Best

Hilary Duff and Mike Comrie are continuing to put family first after their split. The former couple, who finalised their divorce in February, reunited to celebrate their son Luca's fourth birthday over the weekend.

The family were all smiles in a photo Hilary shared on Instagram on Monday, telling fans: "We are so proud of this boy!"

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Hilary Duff and Mike Comrie celebrated their son Luca's birthday together

Hilary also shared a sweet photo of her son tucking into a slice of cake to commemorate his birthday.

"You… are magic my little boy. Happy 4th birthday. My heart just explodes for you," she captioned the image.

Hilary's sister Haylie also joined in the fun with her daughter Ryan, and paid tribute to her nephew and "best big cousin" with a black-and-white family photo posted on Instagram.

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Hilary's sister Haylie joined the family celebrations

"Celebrating my sweet nephew Luca today! I can't believe he is 4!" Haylie wrote. "#HappyBirthday to the sweetest boy & best big cousin. We love you Luc! (also Ryan has a huge mouth full of food in this pic haha)."

Luca's birthday celebrations come just a month after the youngster enjoyed a holiday to Hawaii with both of his parents. The Younger star had documented the trip on social media, revealing that they had been joined by Mike's younger brother Ty Comrie.

"#familyfirst#mauivibes Mikey me luc and @tycomrie," Hilary captioned the family snap.

Hilary and Mike finalised their divorce in February. Legal documents obtained by TMZ reveal that the pair will co-parent their son, splitting joint physical custody, and adhering to a "mutually-agreed upon" set schedule. Neither parent is receiving child support and they have agreed to split any costs related to their son.

Although it has been tough finalising their divorce, Hilary has always expressed how close her and Mike have remained following the split. "We are a unit and we're going to be a unit for the rest of our lives," she told People magazine.