Youtube star Keenan Cahill has tragically passed away aged 27.
A family spokesperson confirmed the news to WGN-TV, stating that he died on Thursday, 29 December.
The internet personality from Chicago, Illinois, made a name for himself lip-syncing to popular songs on the video-sharing platform.
He first rose to fame back in 2010 with his rendition of Katy Perry's 'Teenage Dream', which currently has a whopping 58 million views.
Cahill went on to collaborate with a whole host of famous celebrities as guest artists on his channel, including but not limited to: Jennifer Aniston, 50 Cent, Tinie Tempah, Maroon 5, The Wanted, Justin Bieber and, of course, Katy Perry.
The 27-year-old had Maroteaux–Lamy syndrome, a progressive condition that causes many tissues and organs to enlarge, become inflamed or scarred and eventually deteriorate.
He underwent a number of treatments after being diagnosed at the age of one, including a bone marrow transplant in 1997 and a surgery to relieve intracranial tension.
Earlier this month, he took to Instagram to explain to his followers that he would be undergoing open heart surgery on December 15.
Tributes continue to pour in for the late music star, including from DJ Pauly D, who previously collaborated with Cahill.
Alongside a photo of the pair behind the DJ booth, he wrote: "Rip Keenan... Thank You for always making the world smile."
Writer and director Michael A. MacRae also posted a picture of the two together, stating: "This one stings.
"Keenan was so widely loved for his infectious energy he spread on YouTube. He had a passion to make people smile. RIP, friend. See you again. #rip #gonetoosoon #keenancahill."
Elsewhere, a WGN Morning News producer said: "Sad news: Friend of @WGNMorningNews, one of the first @YouTube sensations, @KeenanCahill passed away after open heart surgery.
"Keenan had over 500-million views. From 2010 to 2014, you could not go to a bar, nightclub or use @Google w/out seeing his image. He was 27. #RIPKeenan."
Fans have shared similarly heartfelt tributes to Cahill, including one who said: "He was such a great talent! Sympathies to his family and friends. RIP @KeenanCahill."
Another commented: "Very sad to hear that Keenan Cahill has passed away. I have fond memories of working with him and his team on 'Hands Up', a collaboration with Electrovamp."
A third added: "Thank you for making so many people smile."
If you have experienced a bereavement and would like to speak with someone in confidence contact Cruse Bereavement Care via their national helpline on 0808 808 1677