Jimmy Fallon serenades Stephen Colbert with a poignant and funny song

Stephen Colbert interviewed Jimmy Fallon on Thursday's edition of The Late Show, and the result was equal parts amusing, nostalgic, and poignant.

In the clip above the pair spend time reminiscing on everything from the various bits they've done together over the years (including the Strike Force Five podcast) to the time they travelled to meet the Pope (Colbert shares the texts he sent Fallon when The Tonight Show host decided to do some comedy bits moments before the Pope was due to walk in the room).