Will Smith has a therapist, and she has a name for his nice-guy persona: Uncle Fluffy. “He signed every autograph, shook every hand, kissed every baby. Fluffy was jovial, talented, smart, generous. Uncle Fluffy needed everyone to like him,” Smith writes in his memoir.

At the Oscars on Sunday night, Uncle Fluffy abruptly left the building. One minute, Smith was sitting in the audience with his wife, Jada Pinkett Smith, laughing along with the host, Chris Rock. Then Rock made the mistake of joking about Pinkett Smith’s bald head: “Jada, can’t wait for GI Jane 2.” The actress has explained in the past that she shaved off her hair after developing alopecia, so the quip was tactless at best.

Smith still appeared to be laughing as the joke landed. But his wife was not. Within seconds, Smith launched himself out of his seat, strode onto the stage and slapped Rock in the face.

At first, the assembled A-listers and audience at home presumed it was staged. But when Smith returned to his seat and shouted: “Keep my wife’s name out of your f—— mouth”, eyes blazing, it was clear that he was deadly serious.

Barely half an hour later, Smith, 53, was on stage again – this time accepting the best actor award for King Richard.

According to reports, the Academy held an emergency meeting once the ceremony was over, with some members demanding that Smith be stripped of his Oscar. On social media, some expressed their anger. Marshall Herskovitz, producer of The Last Samurai and Blood Diamond, tweeted: “I call upon the Academy, of which I am a member, to take disciplinary action against Will Smith. He disgraced our entire community tonight.”

Mark Hamill, the Star Wars actor, called it “the ugliest Oscar moment ever”, while Kathy Griffin, the comedian, said: “Let me tell you something, it’s a very bad practice to walk up on stage and physically assault a comedian. Now we all have to worry about who wants to be the next Will Smith in comedy clubs and theatres.”

Inside the auditorium, however, the mood was different. While Rock retreated backstage to lick his wounds, Smith was consoled by fellow stars, including Denzel Washington, while his PR representative hovered by his side. And when he accepted his award, he did so to a standing ovation. That’s Hollywood.