James DeGale lost his IBF world super-middleweight title after a shock defeat by American Caleb Truax at London’s Copper Box Arena.
The Briton was as short as 1-100 with some bookmakers as he returned to the ring for the first time since January.
But Truax offered constant pressure and rocked DeGale in the fifth as a stiff right drew gasps in the venue.
DeGale, timid for large parts, rallied late on but Truax took the title 114-114 115-112 116-112 on the cards.
Truax sank to his knees on the bell and was convinced he had landed arguably the biggest shock the sport has seen this year.
While DeGale had questions to answer following shoulder surgery in July and having suffered ear and dental damage in drawing with Badou Jack in January, he was expected to shine against the 34-year-old, who was contesting a world title for the second time.
Big money bouts with WBA super-middleweight champion George Groves, or other stellar names at the weight such as Callum Smith or Chris Eubank Jr will likely now have to wait and afterwards DeGale said he hoped for a rematch.
Shortly after the fight, Groves tweeted: “Call it a day, mate, you ain’t got it no more.”
Eubank Jr wrote: “After all the trash talk and disrespectful comments James DeGale you go and put on a display like that! All I can say is WOW! You have properly let down British Boxing #Shameful.”