"And now I want to hand it over to the President of Ukraine who has as much courage as he has determination. Ladies and gentlemen, President Putin," Biden said when introducing Zelensky to the podium on stage.
Biden immediately corrected himself, saying that he was so focused on beating Putin.
The NATO leaders standing behind Putin appeared confused by Biden's mistake as most of them withheld their applause.
A White House press pool reporter in the room said the audience "gasped" at Biden's mistake.
This mishap occurred as Biden faces major backlash in his reelection campaign over concerns about his cognitive state and ability to serve another four years in the White House. Biden, 81, is the oldest US president in history and would be 86 at the end of a potential second term.
A growing number of Democratic lawmakers are calling on Biden to drop out of the presidential race.