A lot of people will be wondering this tonight.
The answer is incredibly simple!
Back in December when Leicester were top of the league and looked as though they would go on and win it, Lineker tweeted this:
YES! If Leicester win the @premierleague I'll do the first MOTD of next season in just my undies.
— Gary Lineker (@GaryLineker) December 14, 2015
And true to his word, on Match Of The Day this evening, he actually did it.
Though some people think they were shorts rather than pants, you have to give him credit for keeping a straight face while Ian Wright and Alan Shearer were laughing at him!
Fair play, Gary!