He has neither confirmed it nor denied it but social media users are convinced Joe Biden used a photo opportunity as a chance to send Donald Trump a cheeky message.
In a picture shared to Twitter by his wife, Dr Jill Biden, the US President-elect can be seen wearing a hat with the words "We just did" embroidered on it, as well as the number "46".
On the same day, defeated Trump, who lost the election to Biden, was seen arriving back at the White House after a game of golf wearing one of his usual "Make America Great Again" hats, with "45" embroided on it.
Trump is the 45th President of the US and Biden will now be the 46th.