Following the screening at Lincoln Center's Alice Tully Hall, Joe Jonas and Demi Lovato emerged for a surprise performance of the romantic duet "Wouldn't Change a Thing," from the movie's soundtrack, with Joe's brothers Kevin and Nick playing backup.
The impromptu concert was a hit, judging by the number of girls in the audience shrieking at the top of their lungs.
Earlier in the event, on the red carpet, Lovato talked about how it's been working with Joe Jonas since their breakup in May. "We've obviously had our ups and downs, but no matter what, we'll be best friends for a long time," she told PEOPLE.
Lovato, who turns 18 on Friday, also expressed her gratitude to Joe, 21, for recently threatening legal action against a blogger who posted a story with alleged falsehoods about their relationship.
"All three of them will defend me, because they're my brothers, they have my back," Lovato said. "And I'll defend them any day, too."
Camp Rock 2: The Final Jam will premiere on the Disney Chanel on Sept. 3 at 8 p.m. ET and air the following three nights at the same time.