Saul 'Canelo' Alvarez acknowledges he faces the biggest test of his career on November 2 when he steps up two weight classes to take on Sergey Kovalev.
Alvarez is a three-weight world champion and is now bidding to take the WBO light-heavyweight belt from champion Kovalev.
The Mexican has lost only once in a 55-fight career (52-1-2) but recognizes the difficulty of facing a bigger man and a fellow established star.
"I'm very motivated here," Alvarez told a news conference. "It's an honor for me to share the ring with a fighter like Kovalev. Now we're about to make history.
#CaneloKovalev Es oficial. Estoy feliz de anunciar que subiré 2 categorías para enfrentar a uno de los rivales más poderosos de esta división . Este 02 de Noviembre será uno de los mayores retos de mi carrera. Vamos a hacer historia juntos. Vamos por 4x World Champion @DAZN_USA pic.twitter.com/0dAaG4Y3Yt— Canelo Alvarez (@Canelo) September 13, 2019
"I know it's going to be the most difficult fight of my professional career. I'm going to put all of my strength and effort to give the best that I can in the ring."
Kovalev described Canelo as "one of the best fighters in the world" and said he was "happy and really excited", while Buddy McGirt, his trainer, paid tribute to both fighters.
"Both of these guys are really true champions," McGirt said.
"I have to say to Canelo: I've always admired you, your trainers did a great job. I really have to take my hat off to you for having the balls to step up and do what real champions do, step up to the challenge.
"Sergey, you're my man, I love you to death. I respect you for accepting the challenge, because you didn't have to. You could have fought any of the other champions.
"The only losers on November 2 will be the people who don't watch the fight."
Kovalev (34-3-1) is returning to the United States, fighting in Las Vegas, after surviving a scare against Anthony Yarde back in Russia last month.