Nathan Fillion Nathan Fillion

The nerds on The Big Bang Theory won't believe that one of their idols is dropping by their show. Seriously, they won't believe it.

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Firefly and Castle star Nathan Fillion will make a cameo appearance on the Feb. 19 episode of CBS's mammoth comedy hit as himself, EW reports. But Leonard (Johnny Galecki) and Raj (Kunal Nayyar) will spend the episode wondering if it's actually Fillion when they run into him at a restaurant. I mean, how does one recognize Captain Tight Pants unless he's attired properly?!

It's the latest geek-cred casting for The Big Bang Theory, which has already welcomed Fillion's Firefly co-star Summer Glau, Wil Wheaton, Carrie Fisher, Leonard Nimoy, and George Takei, among others.

What do you think about this casting?

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