Unbeaten welterweight Floyd Mayweather Jr. announced his retirement again Friday, with boxing’s unofficial pound-for-pound king saying he no longer has the passion necessary to fight.

Mayweather, an Olympic bronze medalist who has won belts in five weight classes, made the abrupt announcement in a letter to select media members Friday. The 31-year-old WBC welterweight champ (39-0, 25 KOs) hasn’t fought since beating Ricky Hatton last December, but was widely expected to take on Oscar De La Hoya in September in a rematch of the richest fight in boxing history.

“This decision was not an easy one for me to make, as boxing is all I have done since I was a child,” said Mayweather, the son and nephew of three of the sport’s top trainers. “However, these past few years have been extremely difficult for me to find the desire and joy to continue in the sport.”

Mayweather also said he was done fighting after each of his last two bouts, but his letter somberly described the reasons for his decision to “permanently retire from boxing.”

“I loved competing and winning and also wanted to continue my career for the fans, knowing they were there for me and enjoyed watching me fight,” Mayweather said. “However, after many sleepless nights and intense soul-searching, I realized I could no longer base my decision on anything but my own personal happiness, which I no longer could find.”

Though Mayweather reportedly earned more than $50 million combined for his split-decision win over De La Hoya and a knockout of Hatton last year, he has seemed much more interested in being a celebrity and a mogul than a fighter over the past 18 months, perhaps best evidenced by his self-proclaimed nickname change from “Pretty Boy” to “Money.”

In the past year alone, he has appeared on “Dancing With the Stars,” worked on his record label, served as the honorary starter at the Indianapolis 500 and entered the wrestling ring for a choreographed tussle with the 440-pound “Big Show” at WrestleMania in Orlando, winning that bout with a set of brass knuckles.

“Floyd was a very talented fighter, no question about it, but he got to a particular point where it was just for the money,” said Bob Arum, Mayweather’s longtime promoter with Top Rank before the boxer began promoting his own career. “Which is all right, it’s a professional sport, but there’s nothing wrong with his decision. It’s a rational decision.”

Though fans and promoters have clamored for Mayweather to take on unbeaten welterweight Miguel Cotto or another top competitor in perhaps boxing’s deepest division, Mayweather had repeatedly dismissed the idea. Instead, his representatives were in discussions for another fight with De La Hoya.