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

Kevin Mazur/WireImage
Shawn MendesĀ 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: