Michael Rapaport is finally coming clean about his beef with LeBron James … saying it all goes back to how The King treated his 2 sons back in the day.

“When they ran into LeBron, he dissed my kids,” Rapaport said on The Breakfast Club.

“He gave ’em the f**kin’ Heisman and turned his back to them.”

Mike thinks ‘Bron held a grudge against him ’cause their friends of friends had a bad falling out … and took it out on his boys.

Rapaport couldn’t believe it – and says that makes LBJ the worst celeb he’s ever met.

“It has nothing to do with a 10 and an 8-year-old … don’t play me and my kids.”

“Out of all the athletes, out of all the celebrities, out of all the rappers I’ve ever met – especially with my kids – that was the only motherf**ker that ever did that. And I was like, ‘Hell f**kin’ no.'”.