After what must be the biggest Academy Awards blunder in history, the accounting firm in charge of the ballot counting process has issued a statement clarifying its role in the error.

As the 89th Academy Awards neared it's climactic denouement, presenters Warren Beatty and Faye Dunaway announced La La Land was the winner of Best Picture when, in reality, Moonlight had earned the top prize.

Halfway through the La La Land acceptance speech, the error was clarified and the correct card was shown on camera.

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"I opened the envelope and it said: Emma Stone, La La Land," Beatty explained. "That's why I took such a long pause and looked at Faye, and at you. I wasn't trying to be funny."

Los Angeles Times writer Jeffrey Fleishman claimed that midway through the La La Land acceptance speech, a stage hand standing in the wings of the stage said: "Oh f**k. Oh my God. He got the wrong envelope."

PricewaterhouseCoopers, which has overseen the Academy's ballot-counting process for the past 83 years, said: "We sincerely apologise to Moonlight, La La Land, Warren Beatty, Faye Dunaway, and Oscar viewers for the error that was made during the award announcement for Best Picture.

"The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected. We are currently investigating how this could have happened, and deeply regret that this occurred. We appreciate the grace with which the nominees, the Academy, ABC, and Jimmy Kimmel handled the situation."

Much has been made of the reactions and responses to the blunder. Moonlight director Barry Jenkins and Best Supporting Actor winner Mahershala Ali have both commented on the incident.