They were mid-way through their acceptance speeches when the error was announced and the producers and cast of Moonlight were invited to the stage to accept the award.
"The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected", a PricewaterhouseCoopers statement read at the time.
Last year's gaffe was mainly the mistake of PricewaterhouseCoopers, the accounting firm that the Oscars puts in charge of counting ballots and managing the envelopes. "That's just what we do when we try to keep shows clean".
A year on, Jimmy Kimmel - the 2017 host (who is reprising the role again this year) - has spoken freely to The Hollywood Reporter and People about what was going through his mind during that whole ordeal.
Film academy president Cheryl Boone Isaacs sent an email to academy members Wednesday detailing the new protocols for announcing Oscar winners developed after the best-picture flub at last month's Academy Awards. Furthermore, Tim Ryan, the company's USA chairman, said he would be personally involved with the Oscars this year. "And where we got it wrong was on the handing over of the envelope".
A PwC partner gave Dunaway and Beatty the wrong envelope after tweeting backstage. You don't know what has happened'. According to the outlet, the duo appeared at the Dolby Theatre to rehearse the presentation - along with a self-deprecating bit.
TMZ reports that the pair will return during this Sunday's ceremony to present the top prize again, presumably after officials have double, triple, quadruple and quintuple-checked the envelope. Adding the stage manager to the confirmation circle further ensures no more mistakes.