Sarah Michelle Gellar Guest Stars in 'Big Bang Theory' Series Finale: How This Surprise Happened! (Exclusive) - 05-17


"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.