By now you're probably totally obsessed with "I Know What You Did Last Summer," the dramatic duet between teen dreams Shawn Mendes and Fifth Harmony cutie Camila Cabello. The dynamic duo really knows how to deliver a tune both on screen and on record...it's no wonder it's a hit these days. 

We've seen them do it on Kelly & Michael, we've seen them do it on The Late Late Show. And as of last night, we've seen 'em do it on The Tonight Show Starring Jimmy Fallon.

Cabello and her "life coach" Mendes truly tore the house down with some help from the Roots. Who would've thought Questlove would dig this somber tune of teenage romance?

Watch the performance above, then take our quiz, Which Member Of Fifth Harmony Are You? Make sure to click through our list of Mendes' 7 most iconic Vines, too. It is how he got his start, after all.