Warren Beatty and Faye Dunaway came onstage to present the award for Best Picture, in celebration of the 50th anniversary of Bonnie and Clyde.[77] After opening the envelope, Beatty hesitated, eventually showing it to Dunaway, who glanced at it and declared La La Land to be the winner.[78] However, more than two minutes later, as the producers of La La Land were making their acceptance speeches, Oscar crew members came on stage and took the envelopes from those assembled, explaining to them that there had been a mistake. La La Land producer Fred Berger, having heard the news, concluded his brief speech by saying "we lost, by the way".[79][80]
https://en.wikipedia.org/wiki/89th_Academy_Awards#Best_Picture_announcement_error