Selma Blair Celebrated by Sarah Michelle Gellar on Her 50th Birthday: 'I'm Always with You'

Sarah Michelle Gellar/Instagram Selma Blair and Sarah Michelle Gellar

Sarah Michelle Gellar is celebrating Selma Blair on the latter's milestone 50th birthday.

The Buffy the Vampire Slayer alum, 45, shared a throwback snapshot of herself and Blair back in 1998 to Instagram Thursday, revealing that it was taken on Gellar's 21st birthday.

"And today we celebrate your 50th!!!" Gellar addressed Blair in the caption. "If I told that little girl on the right, that the girl to her left was going to be her lifelong friend … she would say 'I know.' "

"From the day I met you I knew you were special and would be by my side for ever. I'm sorry I can't be with you today (gee thanks COVID) and that we are not on our special trip (again thanks COVID) but I'm always with you," Gellar continued.

She ended with shout-outs to Blair's memoir title and the pair's 1999 movie Cruel Intentions: "I love you my mean baby #secretsociety."

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sarah michelle gellar/instagram Selma Blair and Sarah Michelle Gellar

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As for Gellar, she rang in her 45th birthday in April with a mini Cruel Intentions reunion, joining pals Blair and Ryan Phillippe for artist Sam McKinniss' exhibit inspired by the 1999 teen film at Jeffrey Deitch Gallery in Los Angeles.

"Art and surprises on my birthday. What a special day," Gellar wrote on Instagram, posing with Blair and Phillippe, 47, in front of paintings depicting Kathryn and Cecile's (Gellar and Blair) kiss and Sebastian's (Phillippe) naked rear.

Gellar stars in Cruel Intentions, based on the 1782 novel Les Liaisons Dangereuses, as Kathryn Merteuil, a rich Upper East Side teenager who makes a bet with her stepbrother Sebastian Valmont that he can't seduce the new principal's daughter Annette Hargrove (Reese Witherspoon).

Blair costars as naïve teenager Cecile Caldwell, whom Kathryn makes a game out of manipulating in order to get revenge on an ex-lover.

RELATED VIDEO: How Selma Blair's Friends Like Sarah Michelle Gellar and Jaime King Have Rallied Around Her

In Cruel Intentions, Gellar and Blair famously lock lips — and the scene is so iconic it was recently recreated in the "Taste So Good" music video for Cann and Weedmaps' Pride Month campaign, more than 23 years after the movie first premiered.

Gellar recently told PEOPLE that she doesn't need an excuse to pay homage to the scene with Blair. "I mean, why wait? We do it all the time. I love that girl," the Golden Globe nominee said about kissing her former costar and dear friend. "She has a very smooth, very easy face to kiss."

In "Taste So Good," Hayley Kiyoko and RuPaul's Drag Race season 14 alum Kerri Colby reenact the now-iconic scene.

"Complete with spit. Because that's the key to it, you've got to get the spit. That's the hardest part," Gellar joked about the recreation in the video, released May 31.