Shawn Mendes and Fifth Harmony’s Camila Cabello have teased their upcoming joint effort -- which is lengthily titled “I Know What You Did Last Summer” -- on Twitter, posting a 15-second teaser of the song and video. By Camila’s own admission, they wrote the track backstage at one of the shows on Taylor Swift’s 1989 World Tour. It makes sense — Shawn opened for Taylor (along with Vance Joy and HAIM), and Taylor welcomed Fifth Harmony to the stage as one of her many musical guests.

Camila’s excitement eventually led to excessive CAPS-lock yesterday (November 10), when her tweets about the song went from "been writing songs in hotel rooms for years and can't tell u how much it means to me to get to share this with you guys. we wrote this together backstage at one of Taylor's 1989 shows out of a random jam session" to "OH MY GOD IM SO NERVOUS/ EXCITED FOR YOU GUYS TO HEAR IT IM GOING TO POP A GASKET!!!"

Shawn also revealed on Twitter that the track will be part of the reissue of his album Handwritten, which is set to include a few brand-new songs as well as a handful of live recordings. According to Billboard, the album will include 16 songs total, and the live tracks were recorded during Shawn’s show at the Greek Theater in Los Angeles on August 16.

Check out the teaser for "I Know What You Did Last Summer" above.

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