Wales' Nathan Cleverly is to defend his WBA light-heavyweight title against Badou Jack on the undercard of Floyd Mayweather's fight with Conor McGregor in Las Vegas on August 26.
His first defence of the title has long been under negotiation but its confirmation represents a chance for him to succeed against an opponent George Groves and James DeGale could not overcome.
Jack, of Sweden, in January spoke of his plans to step up from super-middleweight after his dramatic draw with DeGale, having already outpointed Groves in 2015.
The 30-year-old Cleverly has struggled to rediscover the momentum lost in the first defeat of his career, by Sergey Kovalev in 2013, but won his title last October when Juergen Braehmer withdrew with an injury after the six rounds.
Mayweather's protege Gervonta Davis will against Francisco Fonseca make the second defence of the IBF super-featherweight title he so impressively retained against Britain's Liam Walsh in May, while Tyson Fury's one-time opponent Steve Cunningham meets Andrew Tabiti at cruiserweight.
"This is a fight I have wanted ever since Badou Jack moved to light-heavyweight and I'm delighted to fight in Vegas on an event like this," said Cleverly of the match-up at the T-Mobile Arena.
"I've trained long and hard for this fight and I'm ready to be let off the leash. This is the biggest fight of my career so far and I'm going to do a number on Badou Jack on August 26."
Jack previously insisted he had been struggling to make the super-middleweight limit of 168lbs, and said: I'm thankful for this opportunity and I'm excited about getting another shot at a world title.
"To be a part of this event and fighting on this card is historic. Nothing beats it. I'm excited to get back in the ring. I'm getting ready to take that belt, and win a title in my second weight class.
"The biggest difference between past training camps and preparing for this fight is the fact that I was training to get the weight down, now I'm training to build muscle (for 175lbs) and perfect my boxing strategy.
"This will be a tough fight, but I don't see any issues getting through it. I feel confident and fans can expect a win by knockout or decision. He's not leaving with that belt. It's staying right here in Las Vegas."