Lennox Lewis believes Anthony Joshua and Deontay Wilder will regret not fighting each other for the rest of their lives if they fail to agree terms for a massive unification showdown.
The former unified heavyweight champion, who is the last man to hold the Undisputed Champion title, has warned both Joshua and Wilder to make their fight happen.
"It has to happen and they need to negotiate," Lewis said. "If they don't fight each other they will regret it forever and that is because it will become part of a big debate: Would Joshua have won, would Wilder have won?
"I had that with Mike Tyson and I had to tell my manager Frank Maloney to go out and make the fight happen -- I never wanted to be part of a great debate: I wanted people to know who the King was."
However the former champion, who will sit down to discuss his illustrious career for the first time at an intimate, moderated event in September, did welcome the recent speculation that Tyson Fury is prepared to fight Wilder, perhaps as soon as November.
"It's the right move, right now for Fury," Lewis insisted. "He's standing up for Britain like I did and I have to give him all the respect for agreeing to take Joshua's place and fight Wilder.
"We all wanted Joshua to take the fight, but it's good news that Fury is prepared to accept it and if he wins it would be a great win -- he would have shown the heart of a champion, a real champion."
Lewis had one obstacle during his own remarkable career and he failed to secure a fight with Riddick Bowe, who was a champion at the same time. Bowe had lost to Lewis in the Olympic final in 1988 and their rematch as professionals was on and off for nearly a decade.
"Bowe never wanted the fight, his manager never wanted the fight and they made so many ridiculous demands. It was truly impossible, they demanded millions and millions. The truth is they had no intention of ever making the fight happen," Lewis said.
The 52-year-old will relive his glory days at the O2 in London in September and will share with fans some of the secrets that have been buried since he retired in 2004.
"Every era needs a King and the King is coming to talk - I will talk about these three (Joshua, Wilder and Fury) and believe me if I had to fight either of them I would win: I never got in the ring to lose."
Undisputed: An Evening With Lennox Lewis takes place on Thursday Sept. 6.