Shawn Mendes' duet with Fifth Harmony's Camila Cabello was released on iTunes early before midnight on Nov. 17.

Mendes took to Twitter to make the announcement after teasing fans for over a week with video clips and a website dedicated to the collaboration, titled "I Know What You Did Last Summer."

The song, which was set to be released on Nov. 18, is already on the top songs list on iTunes, making it to the No. 3 spot. Mendes thanked fans for making the song a hit by tweeting, "Im so happy you guys like it. Thank you for being so sweet. I LOVE YOU!!"

Cabello, who kept track of the song's climb from No. 22 to No. 3 on iTunes, expressed her gratitude over the positive response and success of the song, which she and Mendes co-wrote.

"#3 on iTunes. @ShawnMendes thank you. thank you. thank you spelled backwards. thank you upside down. in all the ways, thank you," Cabello tweeted.

On Nov. 13, Mendes released a behind-the-scenes video on his YouTube channel that revealed how he and Cabello recorded the song.

In the video, the 17-year-old said there were a lot of people in his dressing room when he and Cabello began playing around with lyrics and music.

The two teenage stars ended up writing the chorus and had a concept of the full song in about 30 minutes, which Mendes called "spontaneous and random." Cabello can also be heard in a voice over explaining what the song is about.

"The writing process is I think what made this song such an unforgettable experience for me because it was so organic and it was so about two people who started jamming out," Cabello said. "It's basically a conversation between two people in a relationship where its dying but nobody wants to admit that its dying."

Check out the new duet below.