The long-awaited showdown between Oscar de la Hoya and Floyd Mayweather has been confirmed for 5 May in Las Vegas.
Mayweather will risk his unbeaten record against De la Hoya
De la Hoya, 38-4 with 30 knockouts, will defend his WBC light middleweight crown against WBC welterweight champion Mayweather (37-0 with 24 knockouts).
"This is what boxing is all about," said De la Hoya.
"Fighting Mayweather is the type of fight that truly gets me motivated to make the sacrifices I have to make to be the best."
I respect everything Oscar has accomplished in this sport but this time he's in over his head
Mayweather, a world champion in four weight classes, said: "I'm excited to get this opportunity to once again show why I'm pound-for-pound the best in the world and to add another title to my collection.
"I respect everything Oscar has accomplished in this sport, but this time he's in over his head."
Americans Mayweather and De la Hoya, a champion in six classes, could rival records for pay-per-view and live gate income with ringside seats going for $2,000 (£1,020) each.
The Nevada record for paying fans is the $16.8m (£8.57m) spent by a sell-out crowd for Lennox Lewis' heavyweight unification triumph over Evander Holyfield in Las Vegas in 1999.
De la Hoya, 33, last fought in May when he stopped Ricardo Mayorga in six rounds to win the title. Mayweather, 29, is coming off a welterweight title triumph over Carlos Baldomir last month.
De la Hoya is trained by Mayweather's estranged father and said he would understand if Floyd senior felt too uncomfortable to be in his corner.
"I will sit down and talk about this," said De la Hoya. "I want us both to be comfortable with the situation.
"But I am prepared if he says no to me. I am prepared to move on and get somebody else."