Camila Cabello may deny being romantically involved with Canadian pop star Shawn Mendes, but the singer isn't shy about expressing her feelings for her close friend.

On Dec. 20, the youngest member of Fifth Harmony took to Instagram to express her gratitude for being able to perform "I Know What You Did Last Summer" with Mendes at various cities during the iHeart Radio 2015 Jingle Ball tour.

"Thank you to this lovely human @shawnmendes for inviting me to perform during his set on these jingle balls, I had such a blast watching you kill it every night and then coming on to sing IKWYDLS- thank you to you, your team @andrewgertler @stephenschloss (and everyone else who's insta I don't have) for having me," she captioned the photo.

Many fans noticed how affectionate the two stars seemed in several of the photos posted by Cabello, but the star seemed to predict that would happen and made sure to explain what was happening in the photos.

"First to last jingle ball with the Canadian fury. LMAO these pictures make me laugh because we would literally just crack up at the end of this song every night," she wrote.

Along with work on Fifth Harmony's upcoming album, which according to Billboard should be out in early 2016, Cabello has been busy promoting her and Mendes' first single together.

Besides releasing a music video for the song, performing the song live on "The Late Late Show With James Corden," and performing at Jingle Ball, the two will be getting together again to perform at "Pitbull's New Year's Revolution" on Dec. 31 in Miami.

The song, written by Cabello and Mendes, is featured on Mendes' November 2015 rerelease of his album "Handwritten." The song is about a past relationship of Cabello's that went sour.