SPOILER ALERT: A development will conclude tonight's Glee episode that may drive a wedge between Kurt and Blaine.

MEGA SPOILER ALERT: Grant Gustin has been cast in a role that will definitely drive a wedge between Kurt and Blaine.

Michael Ausiello reports that Gustin will portray Sebastian, a member of the Warblers who show sources describe as the "male version of Santana" and make very clear: "He's our villain this season."

Gustin will debut on episode five and go right after Blaine. He's best known for a recent role in the national tour of West Side Story.