The news was announced by Mickelson’s sister, fashion model Meredith Mickelson, who shared a photo of the pair together as children on Instagram.
Tributes to Mickelson have flooded in on social media, with posts from stars including Paris Hilton, Patrick Schwarznegger and Kaia Gerber.
Described as a “rising star”, Mickelson was best known for his role in the US series Mani, and the indie horror film The Killer Clown Meets the Candy Man.