The YouTube community is mourning.

Beloved creator Keenan Cahill died at Ann & Robert H. Lurie Children's Hospital of Chicago, Ill. on Dec. 29, his rep told E! News. He was 27.

"Keenan is a pioneer in social media, becoming one of the first YouTube Influencer's amassing more than 500 million views on his channel and over 1 billion across multiple platforms, traditional media, and live appearances," his rep said in a statement. "Keenan collaborated with Katy Perry, Justin Bieber, Ariana Grande, 50 Cent, the San Francisco Giants, New York Knicks, Jason Derulo, David Guetta, Britney Spears, LMFAO, WWE's The Miz, the cast of GLEE, Tyra Banks, Mike Tyson and many more."

Though Keenan's 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.