King, wearing a sparkly denim jacket, bejewelled with patriotic emblems, then recalled something he once told singer Michael Jackson about assimilation.
"I told Michael Jackson, I said if you're poor, you're a poor negro - I would use the N-word," he recounted. "But if you're rich, you're a rich negro. If you're intelligent and intellectual, you're an intellectual negro."
He then accidentally went there.
"If you're a dancing and sliding and gliding n***er, I mean negro, you're a glancing and sliding and gliding negro."
Some members in the church gasped, while others laughed hysterically.
Trump, who was sitting directly behind King during his remarks, simply smiled at the profanity.
But King carried on, undeterred, leaving many to wonder whether he'd slipped it in there intentionally.
"So dare not alienate because you cannot assimilate, so you are going to be a negro 'til you die," he said.
Trump later thanked and hugged King as he took the stage.
"Ah, there's only one Don King, only one Don," he said.
King was invited to speak at the Republican National Convention in July, but was prohibited by RNC chairman Reince Preibus, who told Trump that the party could not associate itself with him as he was once convicted of manslaughter.
King supported Barack Obama in the 2008 and 2012 presidential elections but is throwing his full support behind Trump in the 2016 election.
