"Joe, you know I won."
Social media users are guessing what former President Donald Trump wrote to his successor Joe Biden after he revealed he'd left him a "private" letter.
During the transition of power in the US, it is a tradition for outgoing presidents to leave a note to their successors.
Trump broke a series of traditions during the transfer of power to Biden's administration, including insisting the result of the November election was fraudulent, and never acknowledging his successor's win.
