The Oscars awards were overshadowed by an extraordinary blunder that saw the Best Picture award mistakenly handed to La La Land before organisers admitted the true winner was Moonlight.
After a night of chaos it appears the unprecedented error was caused by auditors at PriceWaterhouseCoopers who handed the wrong winner's card to presenters Warren Beatty and Faye Dunaway .
Here we break down exactly what went wrong - and how it happened.
How did the wrong winners get announced?
Award presenters Warren Beatty and Faye Dunaway were handed an envelope containing the name of the award winner moments before walking onstage - but they were given the wrong card.
Instead of being given the 'Best Picture' winner they were handed a spare card for the Best Actress, which had already been presented to Emma Stone for her role in La La land.
Footage from the night shows a Beatty checking inside the envelope again in confusion in awkward scenes onstage.
He then passed over the card to Dunaway who read out the only film name on it - La La Land.
The cast has already begun giving their victory speech before auditors at PWC stepped in to announce the mistake.
Whose fault was the mix-up?
The error lay with accountants at PWC - the very firm charged with ensuring that the voting and awards process is accurate and fair.
Firm representatives Brian Cullinan and Martha Ruiz personally oversaw the vote counting.
They were also in charge of transporting the top-secret list of winners to the ceremony and handing the correct envelopes to the presenters.
One of the two would have handed the card to Beatty and Dunaway just as they walked onto the stage to ensure the winner remained a secret to the very last moment.
So how did the wrong card end up with the presenters?
It appears to be a simple case of human error.
Either Mr Cullinan or Ms Ruiz, who stand at either sides of the stage throughout the ceremony to dole out the winners cards, seems to have given the presenters the spare Best Actress card instead of the Best Picture winner.
The pair can be seen standing on stage looking at the card shortly after the wrong award winner was announced.
PWC has apologised and says it is investigating to work out exactly what went wrong.
Why are there two sets of the winners' cards?
Two identical sets of the winner's cards are made for safety purposes as part of strict measures to ensure the ceremony runs smoothly.
The extra set is created in case one of the sets is compromised or stolen on the way to the ceremony.
What was the upshot of the blunder?
The mistake was announced in stage and La La Land's producers graciously conceded the award to the Moonlight team.
But it is a huge embarrassment for PWC.
In interviews given ahead of the awards Ms Ruiz conceded that the held a "big responsibility" for the smooth running of the night.
Speaking about the protocol in the case of an error, Mr Cullinan acknowledged that no one wanted a "Steve Harvey moment" - a reference to a famed mistake at the 2016 Miss Universe pageant when the wrong winner was named onstage.
"They would probably have to take a pause in the show" in such a scenario, he said.
"They would make a correction, probably right then on stage and do it live. Because you wouldn't want to much time to pass if it were the wrong winner."