The firm which is charged with counting the Oscars ballots has apologised for the huge mix-up which saw La La Land announced the winner of Best Picture instead of the correct winner, Moonlight.
Financial services firm Pricewaterhousecoopers (PwC) confirmed presenters Faye Dunaway and Warren Beatty were handed the wrong envelope.
"The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected," the firm said in a statement.
"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."
The mistake rocked the Oscars ceremony, which saw Dunaway erroneously announce La La Land as winner of the award.
The film's director Damien Chazelle led the cast and crew up on stage, and speeches began. It was soon realised, however, that the wrong name had been read out.
The actual winner of best picture was Moonlight.
A production manager could be seen walking onto stage and conferring with the supposed winners.
La La Land producer Jordan Horowitz then announced: "There's a mistake. Moonlight, you guys won Best Picture. "This is not a joke, I'm afraid they read the wrong thing.
"I'm going to be really proud to hand this to my friends from Moonlight."
The shocked Moonlight cast and crew then came to collect their awards.
Beatty was pictured on stage holding the envelope for Best Actress, which had Emma Stone written in it for her La La Land win.
An Oscars representative said they "double up everything" for security reasons, but this is the first time they have faced this problem.
Host Jimmy Kimmel stayed upbeat as he told the crowd: "It's just an awards show - I knew I would screw this show up, I really did."
La La Land star Emma Stone joked about the incident in the Press Room backstage, asking the waiting media, "did you guys see that?".
Moonlight director Barry Jenkins told media immediately after the ceremony that he hadn't yet been given an explanation for the mixup.
He credited the La La Land team for handling the situation well.
"The folks from La La Land were so gracious. I can't imagine being in their position and having to do that."