Mendes, 18, shared a black-and-white clip on Instagram in which the pair was singing Sheeran's track "Kiss Me".
"Found this gem deep in the iPhone videos," Mendes captioned it, adding, "lol I love the 'killed that' face we both make at the end @camila_cabello."
The duo seemed to have intense chemistry as they effortlessly nailed the hook of the song from Sheeran's debut album.
This is not the first time Cabello, 20, and Mendes have collaborated, they previously teamed up for "I Know What You Did Last Summer" in November 2015.