Saul 'Canelo' Alvarez will aim to become a four-weight world champion when he takes on Sergey Kovalev on November 2.
A third meeting between Gennady Golovkin and Canelo had been rumoured but negotiations fell through, leading him to instead move up to take on WBO light heavyweight champion Kovalev.
Canelo, whose last bout was a unification win over fellow middleweight Daniel Jacobs, described Kovalev in a tweet announcing the clash as "one of the most powerful rivals in this division".
Kovalev, 36, has been beaten in three of his past seven bouts but will not shirk the challenge of facing Canelo, with their clash to be staged in Las Vegas.
Canelo's promoter, Eric Gomez of Golden Boy Promotions, explained that the agreement was very difficult to make - because there were parties trying to stop the fight.
Top Rank, who have an exclusive content deal with ESPN, have options on Kovalev and there was a financial tussle over their fee to allow Kovalev to face Canelo on the DAZN streaming service.
“Getting this done has been so, so difficult,” Gomez told Yahoo Sports. “There were a lot of vultures and rats involved who tried to mess things up. Once we got rid of them, we were able to get a deal done with [Kovalev promoter] Kathy Duva fairly quickly, but there were so many outside influences who were trying to sabotage this fight, I almost can’t believe it.
“We’ve worked on this for two, 2 1/2 months. I thought the Golovkin negotiations were difficult, but this beats them all.”
Kovalev is not as invincible as he once appeared to be a few years ago, but he's still a much bigger man and a dangerous opponent.
“Canelo saw something and like the greats, they see things sometimes the rest of us don’t,” Gomez said. “I feel his best weight is middleweight, but he’s the kind of guy who wants to try to take on the toughest challenges he can.”