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 PwC, which has been overseeing Academy Awards balloting for 83 years, to confirm that Beatty and Dunaway received the wrong category envelope.

The Academy of Motion Picture Arts and Sciences, which runs the Academy Awards, said in a statement it is reviewing PwC's role in the ceremony.

PwC said it took full responsibility and apologised 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.


PwC has led the Oscars balloting process for 83 years and two of the firm's US partners, Mr Cullinan and Martha Ruiz, oversaw the vote-tallying process this year.

One of the PwC accountants, Brian Cullinan, centre, after handing the wrong envelope to Warren Beatty. AP

An embarrassed Beatty carried the envelope to the glitzy Governor's Ball after the show, with the writing clearly saying "actress in a leading role." La La Land star Stone had been awarded that Oscar moments before.

"Except for the end, it was fun," Kimmel said overnight, referring to the Oscar show he hosted.

"You know it's a strange night when the word 'envelope' is trending on Twitter," he said on his show Jimmy Kimmel Live.

Reuters