Nick Jonas Joins Demi Lovato for Emotional Duet: Watch

Nick Jonas Joins Demi Lovato for Emotional Duet: Watch

Last night, the Greek Theatre in Los Angeles was transformed into "Camp Rock 3," or at least that's what the ear-shattering screams indicated when headliner Demi Lovato brought out a surprise guest, Nick Jonas.

NICK JONAS AND DEMI LOVATO The pair, who worked together on both "Camp Rock" movies before the Jonas Brothers took Lovato on tour with them, united for a quiet and moving performance of "Catch Me." Lovato took lead vocals as Jonas accompanied her on acoustic guitar, ceding the song to her heartbreakingly tender lead. The JoBro joined her for some brief harmonizing on "Catch," much to fans' delight. "You're so hypnotizing," the pair sang as they gazed into each other's eyes.

Picking up her guitar and brushing her hair out of her face, Lovato brought the house down as the medley segued into "Don't Forget," a song that the pair wrote together in 2008 for her debut album of the same name. "How good does she sound tonight?" Jonas asked as the crowd roared in reply, before the pair leapt at each other in a head-banging, triumphant moment. It concluded with a touching embrace.

The concert was one of a string of summer dates for Lovato, who has woven shows between filming commitments for the upcoming season of Fox's "X Factor," on which she'll be a judge alongside Britney Spears, Simon Cowell and L.A. Reid.

Lovato's most recent single, "Give Your Heart a Break," jumps 19-18 on the Billboard Hot 100 this week. The tune is also her biggest radio hit ever, climbing 17-16 on the Radio Songs tally. Her 2011 album "Unbroken" debuted and peaked at No. 4 on the Billboard 200 and has sold 338,000 copies according to Nielsen SoundScan.

Nick Jonas recently finished a stint on Broadway, playing the lead character in "How to Succeed in Business Without Really Trying." The Jonas Brothers are currently working on new music, having recently parted ways with their label, Hollywood Records. Jonas will be featured alongside brothers Kevin and Joe on the E! reality series "Married to Jonas," which airs this fall.