The YouTube community is mourning.

Beloved creator Keenan Cahill died on Dec. 27, a spokesperson for his family told WGN TV. He was 27.

Though his cause of death has not yet been shared, his last Instagram post, shared Dec. 12, announced that he would be undergoing open heart surgery. “Wish me luck,” Keenan, one of the original viral stars, wrote a week earlier. “Love ya’ll.”

Back in 2010, Keenan—originally known as BeenerKeeKee19952—became an Internet sensation thanks to his lip-syncing videos. Soon, celebrities like Jennifer Aniston, Katy Perry, 50 Cent and Justin Bieber began appearing in his videos, which have amassed millions of views. Plus, he shot a Smartwater commercial with Aniston, performed live with David Guetta, starred in Sara Barilles‘ “Uncharted” space music video, performed at the American Music Awards and collaborated with Ariana Grande. He also released his own original music as well as remixes.

And he did it all while battling the rare auto immune disorder Maroteaux–Lamy syndrome, which stunted his growth and caused swelling of his organs, causing them to become inflamed or scarred, and eventually waste away, according to MedLine Plus.