Mahmoud Charr stopped Christopher Lovejoy in the second round of their bizarre WBA heavyweight title fight in Germany on Saturday night.
Charr unloaded with a flurry of punches at close-quarters, avoiding a Lovejoy overhand right, to score a knock-down in the first major exchange of the fight.
Lovejoy was floored near the corner and could not recover.
The curious fight pitted Charr, who had not boxed since winning a version of the WBA title in 2017, against Lovejoy whose undefeated 19-0 record had been forged entirely in Mexico without any footage of its existence.
Charr's inactivity in the past four years had seen him named 'champion in recess' by the WBA while Trevor Bryan won their 'regular' belt (Anthony Joshua is recognised as the IBF, WBA and WBO champion and is expected to face WBC ruler Tyson Fury to decide the division's No 1).
American Lovejoy had arrived in Charr's home nation this week without a trainer, a cut-man or any team and weighed in at over 21st in Cologne.
He was battling to prove that his claims of being a genuine contender were to be taken seriously - he entered with a fearsome-looking 17 first-round KOs but, against Charr, was unable to do much.
Lovejoy looked troubled when he fell to his knees after an ugly grapple before going back to his corner.
Shortly into the second round, Charr ended Lovejoy's challenge.
Charr, aged 36, has now made a sudden and unexpected return.
He was once a respected contender who beat Britain's Danny Williams and fought Vitali Klitschko and Alexander Povetkin. He had a fight with David Haye fall through.
He was shot outside of a kebab shop in 2015 and has had two hip replacements, but never officially retired after winning his version of the WBA honours in 2017.
Charr's promoter Erol Ceylan told Sky Sports before the fight: "I have big plans for him. If he wins, he could face the winner from Joshua-Fury in the next fight."