Young Hollywood is mourning the death of actor and model Daniel Mickelson. Daniel’s sister and fellow model, Meredith Mickelson, took to Instagram Monday to reveal that her brother died over the Fourth of July weekend. He was 23.

“My heart is shattered & to write this feels so wrong and I don’t even know what to say. Yesterday i lost my brother, best friend & the other half of my heart. There wasn’t a person i loved more on this earth,” the model wrote next to a photo of her and Daniel as children. “There’s no words that can do him justice that I could write. To know him was to love him. He was the happiest brightest smiley most sunshine human to exist and I’m so happy God chose me to be his sister for his whole amazing life.”

Details on what led to Daniel’s death have yet to be revealed.

Stars like Jordyn Woods and Patrick Schwarzenegger commented and offered support and condolences to Meredith and her family, writing, “Praying for you,” while model Amelia Gray Hamlin wrote, “I love you forever daniel.”

Paris Hilton and Kaia Gerber took to their Instagram Stories to pay tribute to their friend, Daniel.

“You were such a light,” Hilton wrote next to a black-and-white photo of her partying alongside the young actor. “So sad to hear this bro. RIP.”