Chadwick, who tragically died at the age of 43 in August 2020, was the favourite to win the statue for his work in Ma Rainey's Black Bottom.
He had swept the awards season in the weeks prior, but in what was the biggest awards's season snub, the award went to Anthony - who had chosen not to attend.
Chadwick was expected to win best actor
What made things even more shocking was that the show producers decided to award the category last - suggesting that even they thought Chadwick had won and there would be a big emotional moment.
"This is MAXIMUM chaotic energy," tweeted one viewer, as another added: "Chadwick Boseman doesn’t need an Oscar to prove his greatness.
"His legacy is already bigger than life itself."
Anthony Hopkins was a surprise win for best actor
Nomadland took home best picture which was awarded third from last, a decision which also confused viewers.
Director Chloe Zhao had previously picked up best director, while the best actress award went to star Frances McDormand.
Even in a year when best actress had been wide open, Viola Davis was expected to take home the little gold man for her role in Ma Rainey's Black Bottom, making Frances' win a surprise.
Nomadland took home three of the big awards - best actress, director and picture
It was a big night for the Brits though, with Emerald Fennell winning best original screenplay for Promising Young Woman, Daniel Kaluuya taking home best supporting actor for Judas and the Black Messiah, and Christopher Hampton winning best adapted screening alongside Florian Zeller for The Father.
Regina King's directorial debut One Night In Miami went home empty-handed, however, despite three nominations.
Emerald Fennell won best original screenplay for Promising Young Woman
The 2021 Academy Awards closed out this year's awards seasons after a two-month delay due to the pandemic.
The stars selected for the 2021 shortlist walked a much smaller red carpet, but still bought their A-game when it came to the glitz and glam.
The ceremony was held in two locations - Los Angeles' Union Station and Dolby Theatre - and saw last year's winners, including Renee Zellweger, reveal the stars who this year were taking home a little gold man.
Not only were the awards given out in person, but all the famous faces in attendance - including nominees, their plus-ones and the A-list presenters - were not required to wear protective face mask coverings while cameras were rolling.
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