Gone too soon. Model and rising actor Daniel Mickelson has died at age 23, and after his sister announced his death, celebrities, including Paris Hilton and Kaia Gerber, shared their grief.

The cause of death of July 4th was not revealed. “My heart is shattered & to write this feels so wrong and i don’t even know what to say,” Meredith Mickelson, a model, posted on Instagram Monday. “Yesterday i lost my brother, best friend & the other half of my heart. There wasn’t a person i loved more on this earth. theres 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.”

In January, he launched a fashion brand called Kids Back Home. Celebrities shared their thoughts. Patrick Schwarzenegger told Mickelson’s sister, “Praying for you,” and model Kaia Gerber posted, “I remember that time we sat on the couch and spent the whole day coming up with our own secret language that we continued to speak every time we saw each other. I wish we could go back there. I wish we were still talking in sentences that probably annoyed everyone else but made us crack up every time.”

“So sad to hear this. RIP,” wrote Paris Hilton.