Following the news that Adam Lambert would appear on Glee's upcoming season, X-Factor judge Demi Lovato is also joining the cast.   Demi will play Dani, a struggling artist friend of Rachel and Santana's.  She'll interact with Adam Lambert's character, who's been described as "Kurt's nemesis."   They are expected to perform together as well.

TVLine says Demi will appear in at least six episodes, beginning with the one airing October 3rd.  Her filming will be scheduled around her X Factor duties.   This is Lavato's first major acting role since her Disney show Sonny With A Chance went off the air two years ago.   Today is Demi's 21st birthday.

TVLine