"I Know What You Did Last Summer" is a song by Shawn Mendes and Camila Cabello and the lead single from Shawn Mendes's debut studio album, Handwritten, released on November 18, 2015. It reached the top 20 on the US Billboard Hot 100 and on the Canadian Hot 100. On January 30 I Know What You Did Last Summer hit the Top 10. Mendes and Cabello promoted the song with several televised performances, including on The Tonight Show Starring Jimmy Fallon and at the 2016 People's Choice Awards.
"I Know What You Did Last Summer" was written backstage spontaneously at Taylor Swift's The 1989 World Tour concert on July 10th in New Jersey, in which Mendes was an opening act and Cabello was the surprise guest as part of the group Fifth Harmony. "We were just backstage. There were like 100 people in my dressing room at the time, and it was madness back there, but I had this guitar and I was just jamming out, and we basically wrote a pre-chorus and a chorus in like 30 minutes," Mendes said in a video released about the making of this song. "And we planned to go into the studio, and it was like an 11-hour studio session where we finished writing the song." After a live performance on Live with Kelly and Michael, Cabello said, "We were just kind of jamming out. We weren’t really consciously writing a song. We kind of started spitting out melodies and put lyrics to it; I don't think we knew we had a song."
The artists co-wrote "I Know What You Did Last Summer" with its producers Ido Zmishlany and Noel Zancanella, with Bill Withers receiving songwriting credits for the sampling of his 1971 single "Ain't No Sunshine". Cabello described "I Know What You Did Last Summer" as a "conversation between two people in a relationship where it's dying, but nobody wants to admit that it's dying."
"I Know What You Did Last Summer" debuted at number ninety-seven on Billboard Hot 100 for the chart dated December 5, 2015, and jumped to number fifty-five on the following week. On the week ending January 9, 2016, the song jumped from number forty-six to number thirty-three. The song has since peaked at number twenty for the chart dated January 30, 2016, becoming Mendes' second top 20 single, after "Stitches", which peaked at number four on October 31, 2015.
A music video for the song was released on November 20, 2015, and was directed by Ryan Pallotta. In the video, Mendes, and Cabello, age 17 and 18 respectively at the time of the making of the song and filming of the video, are seen walking through a dark and desolated landscape. Cabello singing about how she cheated on Mendes but tries to convince him she didn't mean to. They keep trying to walk towards each other but aren't moving. They are seen weathering a sandstorm, followed by a snowstorm and a rainstorm which culminates in a standoff of sorts as they desperately attempt to repair their relationship. The music video has over 148 million views, making it Mendes's second Vevo-certified video, and 1.46 million likes as of August 12, 2016.
Mendes and Cabello's first televised performance of "I Know What You Did Last Summer" was on Live with Kelly and Michael on November 20, 2015. They also performed the song on The Late Late Show with James Corden on November 24, 2015, and at Pitbull's New Year's Revolution on December 31, 2015, in Miami, Florida. Mendes and Cabello performed the track again on The Tonight Show Starring Jimmy Fallon on January 4, 2016.
Preceded by a performance of "Stitches", Mendes and Cabello sang "I Know What You Did Last Summer" at the 2016 People's Choice Awards. They also performed together on The Ellen DeGeneres Show on February 17, 2016.
- This is Camila's first single where she is the main artist without Fifth Harmony.
- However, Camila still belonged to the group.
- the song has the same name as the horror film I know what you did last summer.