"I don’t think it’s a coincidence that the anniversary of #btvs is the same week as #internationalwomensday," Gellar wrote on Instagram. "I have always believed that the world is changed by your example, not by your opinion. We have all learned a lot from Buffy, and the best part is, that never ends."
She then shared a quote that her character, Buffy Summers, said in season seven's episode "Bring on the Night": "From now on, we won’t just face our fears, we will seek them out. We will find them, and cut their hearts out one by one. There is only one thing on earth more powerful than evil, and that’s us."
"Scroll through for some behind the scenes pictures, then and now (hopefully there will even be some you have never seen) #buffyslayday," she added.
Charisma Carpenter, who portrayed Cordelia Chase, also took to Twitter to thank all the Buffy fans for their devotion to the show.
"What a ride, We’re 21 today! Thanks to all you die hards out there that make us a big part of your lives. STILL!" she tweeted. "Your love and devotion to our show does not go unnoticed. So grateful! Thank You! ?? #BTVS #BuffySlayDay21st #cordeliachase #cordy #queenc #theoriginalscoobies."