Mayweather and McGregor — kingpins of their sports — will climb into a boxing ring to face each other at Las Vegas’s T-Mobile Arena on August 26.

The 40-year-old Mayweather will be aiming to reach the 50-0 milestone while McGregor is a heavy underdog in the 12-round boxing match. A victory for the Irishman would be a monumental upset.

«Floyd is the greatest of all time and Conor is the master of our sport,» MMA promoter Dana White said. «I thought it would be an impossible deal to do, but it was the right fight at the right time and we got it done.»

Leonard Ellerbe, chief executive of Mayweather Promotions, said the boxer’s team decided to end his 23-month retirement because the clamor for the 154-pound showdown had been impossible to ignore.

«There is not one place I go to with Floyd where he doesn’t get asked the question, ‘Floyd are you going to fight Conor McGregor?’ All Floyd thinks about is fighting Conor McGregor and whipping his ass,» Ellerbe said.

Mayweather announced the fight on his Instagram account with a graphic saying «IT’S OFFICIAL!!!» showing pictures of both fighters and listing Las Vegas as the location while McGregor sent out an earlier tweet stating «THE FIGHT IS ON.»

«Floyd said ‘154 is no problem, I don’t want a catchweight,'» Ellerbe said.

McGregor is the top pay-per-view draw in UFC while Mayweather had been the money-spinner in some of boxing’s biggest bouts, including matchups with Filipino legend Manny Pacquiao and US star Oscar De La Hoya. Mayweather earned $250 million for his fight against Pacquiao.

«There is a different feel from the Pacquiao fight, Ellerbe said. «It is the unknown factor (of fighting a MMA star).»

Neither Mayweather nor McGregor have competed this year. Mayweather retired from pro boxing in 2015 after defeating Andre Berto, while McGregor (21-3) defeated Eddie Alvarez in November 2016.

White said the key to finalizing the fight was luring Mayweather out of retirement.

«Everybody is happy with this deal,» he said. «Nobody is bummed out.»

The boxing format heavily favors the undefeated Mayweather (49-0, 26 KOs), whom many consider to be the best pound-for-pound fighter in the world.

McGregor, 28, will be entering unknown territory as he has not stepped into a boxing ring since he was a teenager.