Jessie J collaborated with Demi Lovato on stage on Wednesday (December 3).

The Brit was performing at the Triple Ho Show in California, with Lovato also on the bill.

However, she surprised onlookers by bringing out the US star for a rendition of the hit song 'Bang Bang'.

Lovato took over Ariana Grande's lines as the crowd were sent into raptures.

Jessie J later said on Instagram to her collaborator: "Been wanting to sing with you forever! Tonight was special."

'Bang Bang' features on Jessie J's 2014 album 'Sweet Talker', with Nicki Minaj also guesting on the track.

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Watch the duet below: