Oleksandr Usyk won a unanimous points decision to end Anthony Joshua's reign as world heavyweight champion in front of the Londoner's home crowd on Saturday, scuppering hopes of a 'Battle of Britain' unification bout with fellow world title-holder Tyson Fury.
The challenger underlined his dominance in the 12th round with a barrage of punches that had Joshua backed up on the ropes.
The impressive Ukrainian triumphed 117-112, 116-112 and 115-113 on the scorecards of the three judges in just the former undisputed cruiserweight world champion's third bout as a heavyweight.
Victory extended Usyk's perfect professional record to 19 fights unbeaten and saw him join Evander Holyfield and David Haye as the only men to win world titles at both crusierweight and heavyweight.
"This means a lot for me. The fight went the way I expected it to go. There were moments when Anthony pushed me hard but it was nothing special," said Usyk, who now follows brothers Wladimir and Vitali Klitschko in becoming a Ukrainian world heavyweight champion.
"I had no objective to knock him out because my corner pushed me not to do that. In the beginning, I tried to hit him hard, but then I stuck to my job."
Joshua had admitted in the buildup Usyk would present his most difficult challenge outside of Fury and it remains to be seen whether a much-anticipated bout against the WBC heavyweight champion, who defends his title against Deontay Wilder in Las Vegas next month - the third time the pair have fought each other following a split-decision draw and a win for Fury.
There is a rematch clause, with Joshua, who has now won 24 and lost two of his professional bouts having previously lost his belts when beaten by Andy Ruiz in New York in June 2019 only to regain the titles in a rematch in Saudi Arabia six months later.
Eddie Hearn, Joshua's promoter, told Sky Joshua was "devastated" and that he had been taken to hospital for medical treatment.
"Congratulations to Oleksandr Usyk. He put in a great performance and the better man won," Hearn added.
"[Joshua] never really got going, he will go to hospital now, I don't know if he has broken his eye socket, it doesn't look great."
But Hearn added: "The fighter in AJ is already talking about winning the rematch."
Joshua later tweeted, writing: "Keep positive even if the world's crumbling in front of you! London I love you & thank you each and every time!"
At 34, Usyk is three years older than Joshua and he was also giving away three inches in height as well as nearly 9kgs in weight.
Joshua appeared relaxed during a protracted ring walk that saw him shaking hands with fans.
But Usyk moved well right from the opening bell and the southpaw staggered Joshua with a powerful left-hand punch to the head in the third round.
Usyk's left hand continued to prove potent throughout a contest where a slimmed down Joshua did not appear to gain much resulting benefit in ring speed while at the same time lacking power in his punches.
By the end of the 10th round, there was swelling under Joshua's right eye.
Usyk backed Joshua onto the ropes late on and appeared poised for a knockout when the final bell sounded.