Demi Lovato joined Jessie J on stage last night for a very special rendition of the UK singer's track, Bang Bang (December 3).

The Really Don't Care singer surprised fans 99.7 NOW!'s 2014 Triple Ho Show in San Jose, California, by coming out to sing Ariana Grande's verse on the smash-hit song.

Video footage has since emerged of their collaboration, with the crowd going wild as Jessie welcomes Demi to the stage.

[related]Miss. J later posted a smiley selfie of herself and Lovato on Instagram, writing next to the image: "Been wanting to sing with you forever! Tonight was special @ddlovato."

Demi also took to Twitter to post a series of shocked face emojis, adding: "That just happened..... Thank you SO much @JessieJ for having me on stage for Bang Bang... It was an honor!"