BOXING icon 'Marvelous' Marvin Hagler has died aged 66.
His wife, Kay, confirmed the sad news on social media late on Saturday night.
The American, widely regarded one of the greatest boxers ever, reigned as the undisputed middleweight world champion between 1980 and 1987.
His 12 title defences rate as the third-longest ever championship reign, while his six years and seven months with the belt is the second-longest tenure for a middleweight.
Kay, with whom he had five children, wrote on Facebook: "I am sorry to make a very sad announcement.
"Today unfortunately my beloved husband Marvelous Marvin passed away unexpectedly at his home here in New Hampshire.
"Our family requests that you respect our privacy during this difficult time.
"With love, Kay G. Hagler."
A boxing Hall of Famer, Hagler was named Fighter of the Decade (1980s) by Boxing Illustrated and twice named Fighter of the Year (1983 & 1985) by The Ring magazine.
He legally changed his name to 'Marvelous' in 1982, after becoming annoyed that American commentators were not using his nickname.
Regarded as one of the best pound-for-pound fighters ever, while his stunning record of 52 KOs in 62 wins see him ranked among boxing's heaviest hitters.
His chin was perhaps his greatest asset, with just one knockdown scored against him in 67 professional fights - with even that still hotly contested by fans and pundits.
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Hagler had initially claimed the middleweight crown in his one and only fight on British soil, beating Alan 'Boom Boom' Minter by third-round TKO at Wembley Arena.
Marvelous went on to be part of some of the biggest matches in fight history, with blockbuster bouts against the other members of the 'Four Kings' - Roberto Duran, Thomas Hearns and Sugar Ray Leonard - on his CV.
He retired with a 62-3 record, and two draws, with the 1987 split-decision defeat to Leonard his final fight - and one that remains one of boxing’s most controversial results.
Oscar De La Hoya paid tribute to Hagler on Twitter, writing: "Saddened to hear about the death of Marvelous Marvin Hagler. One of the greatest to ever step in the ring! RIP Marvelous."
Promoter Frank Warren said: "Boxing lost an all-time great today."
Eddie Hearn wrote: "Rest in eternal peace the Marvelous One!"