"She's playing my love interest, so I'm very, very excited about it," Glee star Rivera, 26, revealed to MTV at the 2013 VMAs Sunday. "We get to sing a song together."
Rivera isn't the only one pleased about Lovato joining the show. Monday, the X-Factor judge Tweeted that she was "Wayyyyy too excited" about joining the cast for season 5.
"I can't believe I'm going back to acting but the best part about it is that I get to act/sing with some of my really great friends," wrote the former star of Disney's Sonny with a Chance.
Back in June, it was reported that Rivera's love interest, played by original cast member Morris, would not be returning as a series regular.
Meanwhile, Lovato's character is expected to make her debut during the highly anticipated Beatles episode and, according to E! Online, the girls will be performing the song "Here Comes the Sun."
Season 5 of Glee premieres Sept. 26 on FOX.