An accountant for the Academy Awards botched the meticulous procedure for announcing the Oscar for best picture when he handed victory to La La Land before declaring Moonlight the real winner, PricewaterhouseCoopers (PwC) said on Monday.

Accountant Brian Cullinan, who media reports said had been tweeting backstage shortly before, gave presenters Warren Beatty and Faye Dunaway the wrong envelope for the movie industry’s top award on Sunday, the accounting firm said in a statement.

In a gaffe that stunned the Dolby Theatre crowd in Hollywood and a television audience worldwide, “Cullinan mistakenly handed the back-up envelope for Actress in a Leading Role instead of the envelope for Best Picture” to Beatty and Dunaway, PwC said.

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

The Wall Street Journal and celebrity website TMZ.com reported that Cullinan had posted a backstage photo of actress Emma Stone on social network Twitter minutes before the mix-up.

The photo, from Cullinan’s Twitter account, was later deleted but was still viewable on Monday on a cached archive of the page. Cullinan could not immediately be reached for comment.

The mistake was not rectified until the La La Land cast and producers were on stage giving their acceptance speeches. It was left to the musical’s producer, Jordan Horowitz, to put things right.

“Guys, guys, I’m sorry. No. There’s a mistake,” Horowitz said. “’Moonlight,’ you guys won best picture. This is not a joke.”

It took three hours for PricewaterhouseCoopers, which has been overseeing Academy Awards balloting for 83 years, initially to confirm that Beatty and Dunaway received the wrong category envelope.

PwC said it took full responsibility and apologized to the casts and crews of La La Land and Moonlight.

“We sincerely apologise to Warren Beatty, Faye Dunaway, (host) Jimmy Kimmel, (broadcaster) ABC, and the Academy, none of whom was at fault for last night’s errors,” it said in its statement.