‘Seinfeld’ actor Michael Richards says his infamous racist tirade was sparked by a heckler telling him he wasn’t funny.

The 74-year-old, who made a fortune and was skyrocketed to global fame playing Kramer on the hit comedy sitcom, saw his career and reputation left it tatters after he was filmed unleashing a tirade of racial slurs during a stand-up show in 2006 at the Laughter Factory in Los Angeles.

He has now told in his upcoming memoir ‘Entrances and Exits’ about the incident that he was hurting from the failure of his post-‘Seinfeld’ sitcom ‘The Michael Richards Show’ – which lasted only eight episodes in 2000 – at the time of the gig, even though six years had passed since it was axed.

Michael says he heard talking coming from the balcony before he exploded in rage, and yelled: “Shut the f*** up!” – to the delight of the audience.

He then heard someone from the balcony call out: “You’re not funny. We don’t think you’re very funny!”

Michael admitted he took the insult “pretty hard” and called it a “solid punch below the belt”.

He swerves detailing exactly what he said during his tirade – which featured him shouting into the audience: “Fifty years ago we’d have you upside down with a f****** fork up your ass” before calling one of his hecklers the n- word.

Michael says in his book: “Of course, looking back at all, I wish I had just agreed with (my heckler.)

“He went low and I went even lower. We both ended up at the bottom of the barrel.”

Michael added the words “You’re not funny” kept running through his mind at the time of the incident, saying: “He laid it out so clearly, so simply, my biggest fear – not being funny.

“Later, I’ll come to realise that all of this, everything he said, is me. His voice is my voice. This is all ME going on. My inferiority sets in. My anger erupts.”

Michael appeared on the ‘Late Show with David Letterman’ to apologise for the incident days after footage of it spread.

He added his ‘Seinfeld’ co-stars Jerry Seinfeld, Jason Alexander and Julia Louis-Dreyfus reached out during the controversy, but he was “embarrassed” and “concerned about the mess spilling onto them”.

The actor also confesses he has had “some regrets” but believes in the “continuity of the soul”, saying: “Screw-ups in life are necessary.”