I originally saw the news on Wetpaint, but it's been reported that Demi Lovato is set to join Glee for the upcoming fifth season as a recurring character.
Lovato would portray a character named Dani, who is a friend of Rachel (Lea Michele) in New York. Gossip Cop has reported via TV Line that the actress/singer is "nearing a deal" (Gossip Cop).
TV Line also reports that she would appear in a six episode arc. Demi Lovato is already a judge on the Fox show The X Factor, so we'll see what comes of this news. For updates and confirmation, visit Gossip Cop.
I could see Demi on Glee singing her butt off, and personally, I wouldn't mind.
Source: Gossip Cop