Demi Lovato Joined By Nick Jonas During Greek Theatre Gig

Some lucky concert goers were treated to a surprise performance during Demi Lovato's Summer Tour at the Greek Theatre in Los Angeles, California on Wednesday (July 18).

Before singing a duet with one of her celebrity friends, the "Skyscraper" songstress showed off the red tips of her hair while dancing around on stage wearing a studded tights, a see-though corset, black ankle boots and a matching leather skirt and jacket.

Demi took a break from singing to tell the audience, "I'm so nervous. I've got friends in the audience and my family is here." then added, "Luckily some of my friends are going to help me out tonight on stage."

The crowd went absolutely wild when the 19-year-old singer revealed Nick Jonas would be joining her to sing "Catch Me" from her album Here We Go Again.

Afterwards, Nick took to Twitter to tell his more than 4 million fans, "What a special night being able to sing with my friend @ddlovato once again."

Demi has remained friends with Nick since dating his older brother Joe Jonas back in 2010.

Enjoy the pictures of Demi Lovato performing at a special concert at The Greek Theatre (July 18).