Pound-for-pound king Floyd Mayweather, four months removed from his historic victory against Manny Pacquiao in the richest fight in boxing history, said Tuesday he will return to defend his welterweight world titles against Andre Berto on Sept. 12 at the MGM Grand in Las Vegas.

Mayweather (48-0, 26 KOs) has repeatedly said the fight, which will be televised on Showtime PPV, will be the final fight of his brilliant 19-year career.

The bout is the last on a six-fight deal he signed with Showtime/CBS in 2013.

“I’m ready to get back in the ring on Sept. 12 and prove again to the whole world why I’m the best ever,” Mayweather said. “I always bring my A-game and this fight against Andre Berto is no exception.

“He’s a young, strong fighter who is hungry to take down the best,” Mayweather added. “Forty-eight have tried before and on Sept. 12, I’m going to make it 49.”

Berto (30-3, 23 KOs), a two-time welterweight world titleholder, who currently holds an interim belt, is just 3-3 in his past six bouts and viewed by many as an easy mark for Mayweather.

He will be a massive underdog but said he plans to knock Mayweather off his undefeated perch.

“I’m coming to kick Floyd’s ass on Sept. 12,” Berto said. “Best believe that I plan to bring it to Floyd and I’m not concerned about what 48 other fighters have been unable to do. Somebody is getting knocked out and it won’t be me. You don’t want to miss this.”

Sports Book William Hill, which originally opened Mayweather as a minus-1,600 favorite two weeks ago, had odds of Mayweather -2,400 / Berto +1,200 on Tuesday after the announcement of the fight. William Hill reported early action has been one-sided, in favor of Mayweather.