LOS ANGELES — The Academy of Motion Picture Arts and Sciences is apologizing to the cast and crews of the films “La La Land” and “Moonlight” for the mistaken announcement of the best picture winner during Sunday night’s Oscars award ceremony.

The Academy’s apology comes after the accounting firm responsible for the integrity of the Academy Awards, PwC, said mistakes were made and its staffers did not move quickly enough to correct the biggest error in Oscars history.

“We deeply regret the mistakes that were made during the presentation of the Best Picture category during last night’s Oscar ceremony,” the Academy said in a Monday statement. “We apologize to the entire cast and crew of ‘La La Land’ and ‘Moonlight’ whose experience was profoundly altered by this error.”

The Academy also apologized to presenters Warren Beatty and Faye Dunaway and to fans watching around the world.

The Academy’s statement noted that PwC, formerly Price Waterhouse Coopers, has been entrusted with handling Oscar votes for 83 years but said the Academy “will determine what actions are appropriate going forward.”

PwC wrote in its own statement that several mistakes were made and two of its partners assigned to the prestigious awards show did not act quickly enough when “La La Land” was mistakenly announced as the best picture winner. Three of the film’s producers spoke before the actual winner, the coming-of-age drama “Moonlight,” was announced.

“PwC takes full responsibility for the series of mistakes and breaches of established protocols during last night’s Oscars,” PwC wrote. It said its partner, Brian Cullinan, mistakenly handed presenters Warren Beatty and Faye Dunaway an envelope containing the winner of the best actress award.

“Once the error occurred, protocols for correcting it were not followed through quickly enough by Mr. Cullinan or his partner,” the statement read.

It did not address in detail which protocols were violated, or say whether a tweet Cullinan sent about best actress winner Emma Stone before the best picture announcement contributed to the mistake.

The firm, which has handled Oscar winner announcements for eight decades, apologized to Beatty, Dunaway, the cast and crew of “La La Land” and “Moonlight,” the Academy of Motion Picture Arts and Sciences, and host Jimmy Kimmel.

“We wish to extend our deepest gratitude to each of them for the graciousness they displayed during such a difficult moment,” the statement said. “For the past 83 years, the academy has entrusted PwC with the integrity of the awards process during the ceremony, and last night we failed the academy.”

The statement came after nearly a day of speculation about how the worst gaffe in Oscars history unfolded. The fiasco launched countless punchlines, memes and a probe of what went wrong.

The mystery deepened Monday afternoon after the Wall Street Journal reported that Cullinan tweeted a behind-the-scenes photo of Stone holding her statuette. “Best Actress Emma Stone backstage!” the tweet read. The tweet, sent moments before the best picture announcement, raised the question of whether the accountant was distracted from the task at hand. Although the tweet was deleted from the social media site, a copy of it was kept by Google and available through a cache page.

The mistaken announcement altered the usual celebration that follows the coronation of a best picture winner. The only Oscars mistake that came close occurred in 1964, when Sammy Davis was given the wrong envelope for best music score winner but made a quick correction.

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