Shawn Mendes & Camila Cabello Announce 'I Know What You Did Last Summer' Duet: Hear a Preview

11/10/2015 by Malorie McCall

Kevin Mazur/WireImage

Shawn Mendes and Camila Cabello attend the 2015 iHeartRadio Music Festival at MGM Grand Garden Arena on Sept. 19, 2015 in Las Vegas, Nevada.

We know what Shawn Mendes and Fifth Harmony's Camila Cabello did last summer.

Cabello revealed that their upcoming collaborative track, "I Know What You Did Last Summer," was written backstage at one of Taylor Swift's 1989 World Tour shows -- maybe the one where 5H was a special guest?

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The two tweeted about the track all Tuesday (Nov. 10) and even released a teaser trailer. They also revealed the release date of Nov. 18. The song will be included on Mendes' Handwritten Revisited reissue.

Below are the highlights of the Twitter reveals and the teaser trailer:

Have a new single coming next week ! Been working on this song for months now and am so excited about it ! #IKWYDLS

— Shawn Mendes (@ShawnMendes) November 10, 2015

It's a secret song from Handwritten Revisited that I co-wrote with @camilacabello97 ! .. #IKWYDLS

— Shawn Mendes (@ShawnMendes) November 10, 2015

we wrote this together backstage at one of Taylor's 1989 shows out of a random jam session #IKWYDLS @shawnmendes

— camEEla cabeYo (@camilacabello97) November 10, 2015

#IKWYDLS IH MY GOD IM SO NERVOUS/ EXCITED FOR YOU GUYS TO HEAR IT IM GOING TO POP A GASKET!!! @shawnmendes

— camEEla cabeYo (@camilacabello97) November 10, 2015