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A vampire slayer, her mystical little sister and a werewolf pal walk into a set somewhere in Hollywood ... "Buffy" fan-demonium ensues! On Thursday, Sarah Michelle Gellar mercilessly teased "Buffy the Vampire" fans with a not-completely-explained photo via Instagram. "I get the best visitors," Gellar, 36, wrote in a caption accompanying the photo of her reunion with former costars Seth Green and Michelle Trachtenberg.

PHOTOS: Costars reunited!

The trio appear to be on a Hollywood set, most likely the one where Gellar shoots her CBS comedy "The Crazy Ones" with Robin Williams. No word yet if Trachtenberg, 28, and Green, 40, nabbed guest-starring roles on the sitcom -- or whether (please, oh please!) a "Buffy" reunion might be planned.

PHOTOS: Sarah's maternity style

Gellar starred as the titular vampire-staking heroine, Buffy Summers, on Joss Whedon's epic, snarky supernatural saga series, which ran on The WB (and then the CW) from 1997 to 2003. "Gossip Girl" star Trachtenberg joined the cast in 2000 as Buffy's little sister Dawn -- actually a mystical "key" pivotal to saving the universe from evil forces. "Dads" star Green, meanwhile, was part of the original cast from 1997 to 2000 as Oz, the werewolf boyfriend of Buffy's witchy best friend, Willow (Alyson Hannigan).

Series creator Whedon went on to become one of the most sought-after writer-directors in Hollywood, whose "Avengers" is one of the highest-grossing films of all time.

PHOTOS: Stars' supernatural pasts!

Gellar mused about the end of the show back in 2003 -- admitting she was ready for a new chapter. "I was 18 when I started the show; I'm 26. I'm married. I never see my husband [Freddie Prinze Jr.]," she told Entertainment Weekly. "This has been the longest span of my life in one place. There've been times where that's been difficult -- you want to pick up and go, try other things, live in different places. It feels right, and you have to listen to that."


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