Sarah Michelle Gellar Guest Stars in 'Big Bang Theory' Series Finale: How This Surprise Happened! (Exclusive)

ETOnline.com - 05-17

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"Is that Buffy the vampire slayer?!" Why yes, Sheldon Cooper. Yes, it is. On Thursday night’s series finale of The Big Bang Theory, fans were gifted with a TV star treat when actress Sarah Michelle Gellar made a surprise appearance in the CBS comedy’s very last episode.