Now 42, Tony Bellew was the WBC world cruiserweight champion in 2016, before he decided to jump up to heavyweight for a brace of bouts with David Haye.
After knocking his heavyweight rival out twice, he came back down to -200lbs for a shot at the undisputed championship against incredible Ukrainian Oleksandr Usyk, who was just 15-0 at the time when they met in Manchester in November 2018.
Usyk would stop the Liverpool puncher exactly two-minutes into round eight, while the Brit was ahead on two of the cards and drawing on the third - 68-65, 67-66, 67-67.
Despite the championship contest not reaching the final third of the fight, Bellew explained how he lost through pure exhaustion alone, with no way of continuing for another four rounds.
The former WBC cruiserweight champion shared, “My greatest asset is my boxing brain and the fact I can adapt and adjust. I’m not aesthetically great to look at, not the quickest, not the strongest, but I’ve got a really good boxing brain.
“I boxed him [Usyk] and I was outboxing him. It gets to round seven and I’m now exhausted. It took so much energy to do what I did to him in the first six rounds that I was completely spent, was done.
“I went back [to the corner] at the end of round seven, I don’t remember anything about round eight. I’m exhausted because he made me exhausted, he was that good.
“The drilling and the footwork that he does, the front foot pressure without even doing it, constantly being in range - it just zapped me. I’ve never been that tired.”
Bellew retired from boxing after that final defeat. Usyk moved up to heavyweight in his very next fight, where he has now won all seven of his bouts in the top division, while also becoming the first undisputed heavyweight champion of the century.
He next fights IBF champion Daniel Dubois in Wembley in July, in what will be the first-ever undisputed heavyweight fight on UK soil.