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Sarah Michelle Gellar Sends BFF Michelle Trachtenberg the Sweetest Happy Birthday Tribute

Credit: SGranitz/WireImage

Sarah Michelle Gellar and Michelle Trachtenberg's friendship is still going strong. While it's been 13 years since the two starred on Buffy the Vampire Slayer together, Gellar showed fans they still keep in touch when she shared a throwback snap to celebrate Trachtenberg's 31st birthday (and threw in a Buffy reference to boot).

"#happybirthday @michelletrachtenberg It's obvious to all of us, that you have found the "key" to not aging (lol see what I did there??) Btw why did we wear so much more makeup when we were younger?? Just asking," Gellar captioned the snap, referring to the ancient, mystical key on the show.

In the split shot, Gellar and Trachtenberg pose together in a throwback photo, with Trachtenberg wearing a black lace crop top and a pink lip, and Gellar rocking a one-shoulder top. In the more current photo beside it, both ladies flash a smile, looking fresh-faced in matching jean jackets.

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Proof that like their friendship, they're only getting better with time.