Joe Fournier has claimed that he once broke David Haye's nose during a sparring session.
And the unbeaten boxer is using his experience in the ring with Haye during their many training rounds as inspiration for beating the former world champion.
Fournier and Haye will fight on Saturday night in Florida, with many fancying the ex-heavyweight champ to stop his close friend when they do meet in the ring.
But Fournier believes it will be competitive, based on their sparring rounds.
"About five years ago me and David were sparring a lot," Fournier told Switchbox TV. "I was his sparring partner, but nobody really knows that.
"I was the first sparring partner he used for his fights with Bellew because I was so light, he always gets his eyes back first so just does volume, then works on cardio and then he starts working with cruiserweights and heavyweights.
"So there was one occasion in Miami where I’ve hit him with a left hook and bang - broken nose – blood literally everywhere
"Imagine if that was a 10 oz glove without headgear, what would really have happened? You do think about it.
"He's going 70 per cent, I'm going flat out trying to survive but it's been six years I've been active and four where he hasn't and you have to think, this is a real match-up!”
But Haye has dismissed the story, saying that it was closer to a routine bloodied nose, and that Fournier is simply using it as a "claim to fame".
“He’s never hurt me, I’ve felt his power," Haye said in an interview with Switchbox TV.
"I think when he bloodied up my nose one time, he caught me with a shot, and it busted my nose a little bit.
"I think that’s his claim to fame.”
And Haye, like many fight fans, sees no possible way that the much smaller and less experienced Fournier can last against him over their eight round contest.
"The only way he can beat me is if he rubs Tabasco Sauce all over his gloves as there is simply no other way," Haye joked.
But he does respect his opponent's skillset, given his ten professional fights, of which he has won nine with another being overruled from a win to a no-contest.
“Joe’s a professionally trained boxer," Haye explained.
"He’s been doing it significantly longer than say the likes of Jake Paul, he’s sparred with real boxers and has been trained by me, so he’s obviously got a bit about him.”
The pair are close friends outside of the ring, with the fight coming together over a boozy meal between the pair on the Greek island of Mykonos.
When Fournier took offence to Haye telling him that a hypothetical bout between the pair would probably go in the favour of the former world heavyweight champion, they quickly agreed to settle it in the ring.
The fight was not approved to take place as a professional fight by the California State Athletic Commission, who instead ruled that the pair would have to compete in an exhibition.
But when the event, set to take place on Saturday night, was moved from the Staples Center to Hard Rock Live in Florida, the new commission approved the fight, and it will now appear on both men's records.
Haye is 28-4 as a professional, and last fought in 2018 against Tony Bellew, when he was stopped in the fifth round.
Fournier, on the other hand, is better known for his outings at light heavyweight and is 9-0, although he doesn't have any victories against any notable opponents.
Haye and Fournier will clash over eight rounds at heavyweight on the undercard of Evander Holyfield vs Vitor Belfort in Florida, with the 45th President of the United States Donald Trump scheduled to be in attendance.
The event will also feature a bout between former MMA world champions Tito Ortiz and Anderson Silva, as well as musical performances and a Verzuz rap battle.
