The Oscars were plunged into chaos after La La Land was wrongly handed the best picture award instead of the actual winner Moonlight in an extraordinary mix-up at film's biggest awards night.
Organisers were forced to halt the producers of La La Land midway through their victory speech to admit that presenters Warren Beatty and Faye Dunaway had announced the wrong winner after being handed an incorrect card.
Accounting firm PWC, which manages the counting and collation of Oscars votes has apologised for its role in the error and said it is investigating how it could have happened.
Shock spread through the theatre as La La Land's producer Jordan Horowitz announced the error to the audience, showing the inside of the envelope as proof.
"There's a mistake. Moonlight, you guys won best picture," he said."This is no joke. I'm afraid they read the wrong thing."
Horwitz then graciously passed the statue to the Moonlight team as they celebrated their victory - but the blunder led to recriminations through the night.
Beatty returned to the stage shortly after the confusion was announced, saying: "I wasn't trying to be funny".
It appears that he presenters was accidentally given two cards - including a spare 'back-up card' for La La Land's Emma Stone, who had earlier been awarded best actress.
That led him to wrongly announce her film as the best picture winner, he later explained.
Accounting firm PWC they are investigating how said presenters were given the wrong category envelope.
Moonlight director Barry Jenkins said he had been shown "two cards" by Beatty following the mix-up.
"He showed it to me and I felt better about what had happened," he said backstage after the awards.
La La Land actor Ryan Gosling appeared to be struggling to contain his shock after the mix-up was announced.
BBC presenter Martha Kearney, who was also at the awards, said the actor's face looked "like thunder" afterwards.
"We were waiting in the queue for our limos and I saw Ryan Gosling standing next to us and on the phone," she told the Today radio programme.
"His face looked like absolute thunder.
"Can you imagine the moment of thinking you'd won Best Picture, to have it snatched away from you?"
Producers of both films attempted to smooth over the historic blunder, with the legendary statuette quickly passed onto its rightful winners.
The extraordinary error caps a season that saw la La Land collect a record-tying 14 Academy Award nominations but also face criticism for 'whitewashing' jazz history with an overwhelmingly white cast.
In contrast, Moonlight follows a young black boy's journey to adulthood through a rough upbringing in Miami with Naomi Harris staring as his drug-addicted mother.
Both films were heavily tipped as likely best picture winners.