Everyone attending the 94th Academy Awards ceremony Sunday was left shocked when Will Smith stormed the stage and slapped Chris Rock.

The Oscar best actor winner was upset because of a joke Rock said about his wife, Jada Pinkett. The comedian said he couldn't wait to see her as "G.I. Jane 2," referencing her shaved head. He made the comment as he presented the award for best documentary feature.

Jada suffers from a condition called alopecia areata, which causes hair loss, but Rock had no idea about it and that he "doesn't have a mean bone in his body," a source told TMZ.

At first, Smith was seen laughing at the joke, but his wife had a rather somber expression, which reportedly prompted the actor to walk onto the stage and slap Rock. The audience first thought it was part of a script. They soon realized it was serious when Rock said out loud, "Will Smith just smacked the s–t out of me."

Though the broadcaster of the event, ABC Network, muted the exchange, the audience could clearly hear him shouting at Rock even after he returned to his seat: "Keep my wife's name out of your f—ing mouth!"

"We thought it was a bit. Then we heard Will yelling. You heard it so loudly in the theater," said one Hollywood insider, according to Page Six.

Another insider explained how she watched the chaos from the green room.

"Suddenly everyone froze and the whole place was, like, what the f—k happened?" she said, adding that Smith's longtime publicist Meredith O'Sullivan Wasson, Academy CEO Dawn Hudson, Oscars producer Will Packer and Academy president David Rubin walked into a private room "very quickly…with great seriousness."

US actor Will Smith slaps US actor Chris Rock onstage during the 94th Oscars
US actor Will Smith slaps US actor Chris Rock onstage during the 94th Oscars AFP / Robyn Beck

"There was a sense that something was wrong with Will. I heard Chris' manager, Jason Weinberg say, 'I've got to deal with the LAPD now. I have to find out what is going on,' then he walked out," said the insider. "Everybody was saying, 'Holy s—t.' Even the bartenders. The gravitas was not lost on anyone. There were people saying, 'Oh, my god, poor Chris.' People were wondering if Chris' face was red because he was flush or because he was hit."

After presenting the award, Rock reportedly left the stage to meet with the producers and cops.

"When he got off stage, he was a bit shaken. He was taken into a side room and talked to producers and LAPD. Then he went to the writers' room and spoke to his guys and left. I mean, these are guys he has worked with for years. No one thought there were any issues with the jokes. If anything, Regina Hall's joke about Will and Jada earlier in the evening (which hinted at their open marriage) was in way worse taste," the insider said, adding that Rock did not have a mark on his face from the slap.

Rock has reportedly declined to press charges against Smith.

Smith, who picked up the Best Actor Award for his role in "King Richard," later issued a public apology to Rock on Instagram.

"I would like to publicly apologize to you, Chris. I was out of line and I was wrong. I am embarrassed and my actions were not indicative of the man I want to be. There is no place for violence in a world of love and kindness," he wrote.