What's happening with Kesha is one of the saddest stories in pop music. In 2013 she accused her producer, Dr. Luke, of sexual assault in a lawsuit. However, her contract bars her from making music ...

Also during the show, Charli and the "One of Your Girls" hitmaker, 29, joined Kesha for a performance of her 2009 classic "TiK ToK." That wasn't the only unexpected guest at the concert.

Kesha's "Joyride" is one of the first top 10 hits ever on Billboard's new Hot Dance/Pop Songs chart, ... [+] where it debuts at No. 10. WEST HOLLYWOOD, CALIFORNIA - MAY 31: Kesha performs onstage ...