Doherty took to Instagram on Friday to share an amazing throwback shot of the pair hanging out at a party, alongside a sweet note thanking Gellar for always "rooting for me."
"Happy Birthday @sarahmgellar I'm posting this pic because of the pure joy and fun, I am clearly having in your presence," she wrote. "From the moment we met, you embraced me, supported me and stood fiercely by my side. Never a moment of insecurity or feeling threatened between us. Instead, you only rooted for me and lifted me up."
"You are that woman that walks in a room and lights it up.... not only with your smile, but with your confidence, humility, intelligence and sense of ease. Naturally, you are an Aries!!!" Doherty continued. "I love you. I'm proud of you. I also want you to come home now so we can celebrate!!! Happy birthday beautiful friend. You deserve the moon and more."
Doherty, who turned 46 on Wednesday, has always supported the Buffy the Vampire Slayer star -- even if it meant taking a photo of her recent TV appearance and posting it to Instagram. In fact, the actress did just that last week, praising Gellar's appearance on Watch What Happens Live With Andy Cohen.
"Sarah you are a class act. From your pinky toe to the top of your head," she captioned the screenshot. "I am so very proud of you and not just for your success with @foodstirs or your amazing career or your new book, #stirringupfunwithfood but for the warm, generous, supportive, loving person you are."