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Demi Lovato Sings Ariana Grande's 'Bang Bang' Verse At Jessie J Concert And Fans Go Nuts

Demi surprises Jessie's fans in California.

You could barely hear Demi Lovato when she took the stage belting Ariana Grande's "Bang Bang" verse at the Jessie J concert in San Jose, California, on Wednesday night. But it wasn't because she was having technical difficulties; you simply could not hear her over the screaming of fans.

Wearing a lacy, black crop top and matching high-waisted skirt, Demi emerged from side-stage to a flood of squeals, singing Ariana's grown-up verse: "She might've let you hold her hand in school, but I'mma show you how to graduate."

During Nicki Minaj's rap -- could you imagine if she was there too? -- the two grooved and bounced around together, and whenever Jessie sang "bad girl," she pointed at Demi. When the party was over, they hugged and walked off stage together. But now that fans have a taste of what the two divas can do with the Sweet Talker track, they want more.