American mixed martial arts (MMA) fighter Kimbo Slice has died aged 42.
The fighter was taken to a hospital in South Miami, Florida, on Monday night.
He'd been due to top the bill at London's O2 Arena next month in a rematch against James Thompson at MMA event, Bellator 158.
"We are all shocked and saddened by the devastating and untimely loss of Kimbo Slice, a beloved member of the Bellator family," said Bellator MMA president Scott Coker in a statement.
Kimbo Slice controversially won his first bout against Brit James Thompson in 2008
"One of the most popular MMA fighters ever, Kimbo was a charismatic, larger-than-life personality that transcended the sport.
"Outside the cage he was a friendly, gentle giant and a devoted family man.
"His loss leaves us all with extremely heavy hearts, and our thoughts and prayers are with the entire Ferguson family and all of Kimbo's friends, fans, and teammates."
Scott Coker tweeted a link to his statement about Kimbo Slice's death., external
British MMA fighter Jack Mason has also paid tribute to Kimbo Slice. He was set to appear with him at the Bellator MMA event in July.
"It's just a sad day really," Jack told Newsbeat.
"Lots of people I know have spent time hanging with him or lived with him in a TUF [The Ultimate Fighter] House, spent time with him at shows and said he was a lovely guy.
"It's sad because he was only 42. It's definitely a young age to pass away at.
Jack said for a sportsman of that age, the pressure was high for a fighter like Kimbo.
"Training day-in day-out is always going to be tough."
"It's definitely a tough sport to be involved in when you're 42 years old. You get beaten up by lots of younger guys on a daily basis.
A sergeant at Coral Springs Police in Miami, Carla Kmiotek, said that the fighter, whose real name was Kevin Ferguson, was admitted to hospital on Monday night.
She says officers were dispatched to his home and said there was no foul play suspected.
A gym where he trained in Coconut Creek, Florida, announced Kimbo Slice's death on Twitter.
They also tweeted a photo of him outside the facility., external
Kimbo Slice was born in Nassau, Bahamas, in 1974 but moved to the US as a child.
He rose to fame through his YouTube street fighting videos, which made him an internet sensation. Rolling Stone called him The King of the Web Brawlers.
In 2009 he signed with UFC but lost his first fight in the 10th series of The Ultimate Fighter against Roy Nelson.
Kimbo Slice meets Mike Tyson at the Spike TV video game awards in 2009
He signed with MMA organisation Bellator last year beating Ken Shamrock and Dhafir Harris.
However, the Dhafir Harris fight was turned into a no contest after he tested positive for an anabolic steroid, Nandrolone, in February.
Kimbo Slice was forced to pay a $2,500 (£1,722) fine and his fighting licence was revoked in Texas.
Kimbo Slice lost to Matt Mitrione in Quebec, Canada, in 2010
His heavyweight rematch against James Thompson next month was being billed as the "tentpole" event at Bellator 158 at London's O2 Arena on 16 July.
The pair's original fight in 2008 was the most-watched fight in the history of mixed martial arts with 7.28 million viewers.
Kimbo Slice won in the third round after the referee controversially stopped the Elite Xtreme Combat contest.
The fighter also won seven boxing bouts between 2011 and 2013 and also acted, appearing in The Scorpion King 3: Battle for Redemption in 2012 as Zulu Kondo.
The fighter has six children and was engaged to long-time girlfriend, Antionette Ray.
One of his three sons, Kevin Ferguson Jr, made his MMA debut in March.
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