Two-time Preston City Wrestling champion Adrian McCallum - known by his ring name Lionheart - has died at the age of 36.
McCallum was the reigning ICW (Insane Championship Wrestling) world heavyweight champion and also competed for WWE and TNA during his career.
He was also a two time Preston City Wrestling (PCW) champion in 2012 and 2013 in the heavyweight division.
Scotland-based ICW said in a statement: "We are heartbroken to learn of the tragic death of ICW World Heavyweight Champion, Adrian 'Lionheart' McCallum."
"Adrian was a mainstay of ICW and British professional wrestling. Most importantly, he was our friend. His passing leaves a huge hole in the lives of those who knew him."
A PCW spokesman took to social media saying: "Rest in peace champ.
"Always be a massive part of our lives and company."
No further details about McCallum's death have been released.
WWE wrestler Cedric Alexander said he was "crushed" to hear of McCallum's death, while fellow WWE star Paige - real name Saraya-Jade Bevis - said she would be "forever grateful" to have known him.
Pete Dunne, the longest-reigning WWE UK champion, tweeted: "I always looked up to Lionheart's professional approach to wrestling when it was far from that at the time. People like him were pivotal in the growth of a scene that has lead to so many people being able to do this for a living."
British wrestler Will Ospreay, who currently competes in Japan, said: "Every time I've met you, you have been nothing but a sweetheart. I honestly cannot believe I'm writing this tweet.
"Devastated doesn't cover how I feel."
Meanwhile, Scottish actor Greg Hemphill, known for appearing in sitcom Still Game, called him a "lovely guy".
"Heartbroken for the whole wrestling family tonight," he said. "What a talent and what a lovely guy. He will be sorely missed."