Saul 'Canelo' Alvarez will move up to cruiserweight to fight Ilunga Makabu for the WBC title in a bid to become a five-weight world champion.
Alvarez's latest move to cement his legacy as one of the greatest fighters of all time comes less than two weeks after he became the undisputed super-middleweight champion by stopping Caleb Plant in Las Vegas.
"The WBC has approved unanimously Canelo to fight for the WBC cruiserweight championship," president Mauricio Sulaiman said.
"This is a surprise to me but I'm sure he will continue to make history."
With just two losses on his 60-fight record, Alvarez is considered by many as pound-for-pound the best fighter in the world, and has already claimed world titles at super-welterweight, middleweight, super-middleweight and light-heavyweight.
Only five men have been quintuple world champions - Americans Floyd Mayweather, Oscar de la Hoya, Ray Charles Leonard and Thomas Hearns, plus the Philippines' Manny Pacquiao. In the women's code, America's Amanda Serrano and Japan's Naoko Fujioka achieved the feat.
Makabu, 34, is on a nine-fight winning streak since suffering defeat by Tony Bellew at Goodison Park in 2016 and is Africa's only current world champion.
The DR Congo fighter has held the WBC title since January 2020, and defended it later that year but is yet to fight in 2021.
In comparison, Alvarez completed a remarkable 12 months of action when he knocked out Plant in the eleventh round of their super-middleweight fight this month.
The Mexican kicked off a thrilling period when he stopped then-undefeated world champion Callum Smith in December 2020. Alvarez was back in the ring in February to see off mandatory challenger Avni Yildirim in three rounds before stripping another unbeaten world champion Billy Joe Saunders of his WBO title in May.
Alvarez, 31, had moved back down to super-middleweight after successfully jumping up to light-heavyweight in 2019 when he knocked out Sergey Kovalev to win the WBO title.
Cruiserweight is the final weight class before heavyweight. The division houses the likes of British duo Richard Riakporhe and WBO belt holder Lawrence Okolie, while Latvia's Mairis Briedis holds the IBF and Ring magazine belts and Frenchman Arsen Goulamirian is the WBA (Super) champion.
Okolie (17-0) was clearly frustrated by the news of Alvarez's move to cruiserweight as the undefeated Briton works to secure a unification fight in 2022.
"That's another belt I can't unify now," he said on Twitter.
"Madly enough I think he will actually win and go back down in weight. So I can go back to being a fan."
He added: "Don't blame me when you see me box [a] YouTuber next."
- The King of Sumo: How this Hawaii-born wrestler took the sport by storm
- Do managers have any sympathy for referees?: Paul Lambert reveals all to Sacked in the Morning