Former US President Donald Trump has brutally roasted US President Joe Biden following his disastrous press conference.

Within minutes of the oldestever sitting president’s presser, Biden called Vice President Kamala Harris, Donald Trump.

The embarrassing mistake happened very early on, with Trump posting to Truth Social about it shortly after.

“Crooked Joe begins his “Big Boy” Press Conference with, "I wouldn't have picked Vice President Trump to be vice president, though I think she was not qualified to be president." Great job, Joe!” wrote Trump.

Biden’s nearly hourlong presser allowed reporters to ask the president any unscripted question.

The press conference followed Biden’s speech at the NATO summit in Washington.