The pair has been friends ever since they toured together with Fifth Harmony star Cabello's ex-boyfriend Austin Mahone last year (14), and now a source tells E! News they are dating.

Over the past few weeks, the singers have been spending more time together and documenting their interactions on social media, even posting a short video of them singing a mash-up of Ed Sheeran's Give Me Love and Destiny Child's Say My Name on Instagram.com.

They fuelled the romance rumours even further over the weekend (20Sep15), when they attended the iHeart Radio Music Festival in Las Vegas, and Mendes sneaked up behind Cabello on the red carpet, while photographers noted she was blushing.