Infamous boxing promoter Don King isn’t holding a grudge against the Rev. Al Sharpton in the wake of a blockbuster report detailing how Sharpton snitched on King to the FBI.

King on Sunday called the revelations about Sharpton’s 1980s work as a paid undercover informant “old news” and praised Sharpton as a “stand-up person” for secretly recording mobsters with a customized Hartmann briefcase provided by the feds.

“Al Sharpton had enough guts to fight, if it is true, to fight for others spending their ways and means to take away opportunity,” King told The Post.

“How many people would put their lives in danger?”

The wild-haired fight organizer wouldn’t say if he ever saw Sharpton carrying the briefcase when they met, or if he suspected that the then-tubby activist was secretly a rat.

“I’m not into mud-slinging,” King said.

But King — who was in Las Vegas for Saturday’s Manny Pacquiao victory over Timothy Bradley at the MGM Grand Garden Arena — hailed Sharpton for painting large X’s on the homes of drug dealers at the time, to identify them to neighbors and cops.

“They should give him five stars for service and duty above and beyond for the betterment of our nation, for this great country of America,” King said.

“The people’s greatest resources are its children, and he put himself in the fight for our youth. He makes us live up to that creed, one man, for liberty and justice for all.”

“I commend Sharpton for his bold, courageous Americanism,” he added.

According to The Smoking Gun website, the FBI “flipped” Sharpton into working as a confidential informant after snaring him in a sting operation in which he was videotaped discussing a drug deal with an agent posing as a South American narcotics trafficker.

In an exclusive interview published Saturday in The Post, former Sharpton crony Robert Curington said the agent initially wanted to meet with King, but King “knew something was off” and had Sharpton talk to him instead.

Curington also said Sharpton jumped at the chance to get in on the agent’s phony deal, saying: “It was greed. He just wanted the money.”

As an informant, Sharpton’s targets included King, who was being investigated as part of a probe called “Crown Royal,” which was shut down when Newsday first exposed Sharpton’s work as an informant in 1988.

Sharpton called Curington’s claims “blatantly wrong” and insisted that he became a snitch due to threats against him by the mob, not because of the drug sting.

Additional reporting by Pedro Oliveira