Donald Trump is a "racist" who asked a group of white golfers if they had "ever f*cked a n****r", according to Hollywood superstar and vocal Trump critic Don Cheadle.

Cheadle made the incendiary allegations during a lengthy back-and-forth on Twitter with supporters of the incumbent president.

The veteran Ocean's Eleven, Crash and Iron Man 2 star was in the depths of a heated debate when one Trump fan accused him of "Trump-hating way before treason" - a reference to the ongoing claims that the New York tycoon won the 2016 election with Russian backing.

"Hated him since he asked my friend's father at a Doral pro-am if he'd ever "f*cked a n****r..." Did it for me ...", Cheadle replied. He was referring to a mixed professional and amateur golf contest at Donald Trump's luxury resort in Doral, Miami.

He went on to claim the unnamed father was playing in a foursome with the billionaire tycoon. The man in question could not be named, Cheadle said, because his daughter was a celebrity.

"The Donald thought they were all 'like minded'," he continued. "Mistook their shock for disgust...

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"He went on to clarify, "No, no, it's great!" and some more stuff before they just teed off in silence."

Asked why he had not mentioned this story during the Presidential campaign, Cheadle said he didn't think it would have made any difference.

"Many already know this to be in his nature. It's not hidden. And those who can't see it, might never. The story would have changed little," he wrote.

This was not the first Twitter tirade Cheadle has directed against the billionaire tycoon.

In 2016, he called the then-Presidential hopeful a "POS" (piece of shit) who should "die in a grease fire" after he used the shooting death of black woman Nykea Aldridge to claim "African-Americans will VOTE TRUMP!"

Mr Trump has faced multiple accusations of racism: he was sued for allowing his organisations to discriminate against black tenants, and his casinos were fined for allowing wealthy white gamblers to send black employees from the table.

He has also allegedly said that "laziness is a trait in blacks", and accused Mexican migrants to the US of being "racist".

When a fan said they were shocked a public figure would make such comments, Cheadle replied: "He wasn't the president then. Just a racist, misogynistic, draft dodging, "birther" conspiracist, pussy grabbing, bankruptcy machine..."