Sarah Michelle Gellar is paying homage to her late friend and "Buffy the Vampire Slayer" co-star Michelle Trachtenberg.

On what would've been Trachtenberg's 40th birthday, Gellar took to Instagram to share a few kind words about the actor who died earlier this year.

"When you turned 16, it was hard not to still see you as the little girl I met on All My Children," she said. "When you turned 21, I had to teach myself to not see you as the little sister anymore. I can’t imagine what 40 would have been like."

"This I know… it would be filled with love. Happy birthday @michelletrachtenberg," she added.

Sarah Michelle Gellar and Michelle Trachtenberg at a "Buffy The Vampire Slayer" reunion. Jean-Paul Aussenard / WireImage

Gellar accompanied her post with a heartfelt video of her huggin

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