Nathan Fillion to Guest Star on THE BIG BANG THEORY

According to Entertainment Weekly, CASTLE star Nathan Fillion will make a cameo as himself on CBS' hit comedy THE BIG BANG THEORY.

In the episode, "Raj (Kunal Nayyar) and Leonard (Johnny Galecki) see him sitting at a restaurant and debate whether or not it's really him and whether or not they should ask him for a picture." Fillion will appear on the Feb. 19 episode.

Leonard and Sheldon are brilliant physicists - geniuses in the laboratory, but socially challenged everywhere else. Enter beautiful, street-smart neighbor, Penny, who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten engaged. Even Sheldon has found a female companion, entering into a "Relationship Agreement" with neurobiologist Amy Farrah Fowler. In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Koothrappali, Wolowitz and Wolowitz's adorable microbiologist wife, Bernadette.