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.