Barry Jenkins' Moonlight was in fact given the accolade, in an unbelievably surreal piece of television and undoubtedly the most dramatic moment in Oscars history.
Presenters Faye Dunaway and Warren Beatty announced La La Land as the winner of the night's biggest award, with cast and crew flooding the stage.
Producer Jordan Horowitz launched into an acceptance speech, getting quite far into it, before the truth slowly spread through the gaggle of people on the podium.
Speaking into the microphone, Horowitz announced: "There's a mistake. Moonlight, you guys won best picture." As the crowd looked on, bemused, he reiterated: "This is not a joke. Moonlight has won best picture."
After host Jimmy Kimmel attempted to crack jokes ("Warren, what did you do?") to break the tension, Beatty explained: "I opened the envelope and it said: Emma Stone, La La Land. That's why I took such a long pause and looked at Faye, and at you. I wasn't trying to be funny."
Jenkins, understandably blindsided, took the stage and tried his best at saying a few words: "Even in my dreams this could not be true. But to hell with dreams! I'm done with it because this is true, oh my goodness."
The director added: "And it is true, it's not fake. We have been on the road with these guys for so long and that was so gracious, so generous of them. My love to La La Land. My love to everybody. Man." (Read the full transcript here.)
Though the gaff was initially pinned on Beatty/Dunaway, it appears it was a crew member's responsibility to ensure the correct envelopes make it on stage.
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An official statement has since been delivered, clarifying that the company entrusted to manage the winning envelopes was at fault.
“The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected," PricewaterhouseCoopers said. "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."
Steve Harvey quickly started trending, his infamous Miss Universe screw-up having been well and truly upstaged:
Many joked that maybe Hillary Clinton did win the presidential election after all, and M. Night Shyamalan had fun with the moment too:
Soon after the award was announced, another twist as Emma Stone revealed she was holding her Best Actress card the entire time.
“I f***ing loved Moonlight. God, I love Moonlight so much," she told press backtage. "I’m so excited for Moonlight! And, of course, it was an amazing thing to hear La La Land. I think we all would have loved to win Best Picture.
“But we are so excited for Moonlight. I think it is one of the best films of all time. So I was pretty beside myself. I was also holding my Best Actress in a leading role card that entire time.
“So whatever story - I don’t mean to start stuff - but whatever story that was, I had the card. So, I’m not sure what happened. And I really wanted to talk to you guys first.”
Reacting on Twitter, Jenkins wrote how he was still speechless over the win, posting a photo of the Moonlight announcement card alongside the message.
Mahershala Ali - who won Best Supporting Actor earlier in the night for his role in Moonlight, also commented on the situation.
“La La Land has done so well and has resonated with so many people," he told press. "When their name was read, I wasn’t surprised, and I was really happy for them. When I did see security or people coming onstage and their moment was being disrupted in some way I got really worried and then when they said 'Moonlight, you guys have won.' It just threw me, more than a bit.
"I didn’t want to go up there and take anything from somebody. It’s very hard to feel joy in a moment like that … but I feel very fortunate for all of us to have walked away with the best picture award. It’s pretty remarkable."
Beatty has previously announced the Best Picture winner on two occasions - once in 1975 and again in 1990. However, it was Dunaway's first time announcing the award; the Bonnie and Clyde star has so far refused to comment on the event.
The shocking twist, itself worthy of an award, capped off a slightly disappointing night for La La Land, which also failed to pick up many of the technical awards it was expected to, though the film did pick up Best Director, Best Actress and Cinematography. In total, Chazelle's film took home six awards.
Moonlight meanwhile, in addition to the night's biggest award, ensnared Best Supporting actor thanks to Ali along with the Original Screenplay prize.
Hacksaw Ridge picked up an unexpected number of awards, taking two in total, while the critically-panned Suicide Squad is now an Oscar-winning film (if just for Hairstyling and Make-up).
You can read the full list of winners here.
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