Chris Pratt is celebrating being a dad to a teenager. On Sunday, the Guardians of the Galaxy star shared a post on his Instagram Stories to mark his son Jack's 13th birthday. "I have a teenager???" Pratt wrote in mock disbelief over a collage of photos of himself with his son, whom he shares with ex-wife Anna Faris. "Jack, I can't believe you are 13 today. I've watched you grow into such an incredible young man, and am truly proud of the person you are becoming. I love you!" he penned. The collage featured photos of the father-and-son pair posing in matching jerseys with 'Pratt' on the back, visiting a farm, attending sporting events and working on DIY projects together. Pratt and Faris split in 2017 after tying the knot in 2009. Their divorce was finalised in 2018. The former couple welcomed Jack in August 2012. The Marvel alum shares three more children with his wife, Katherine Schwarzenegger. Pratt previously opened up to Entertainment Tonight about the sweet connection between Jack and his younger siblings. "There's a big age separation. He does a great job, he's so sweet with them," he said of his eldest child. "And they love him so much, and they miss him when he's gone."