See Sarah Michelle Gellar's birthday tribute to 'fiercest friend' Shannen Doherty

/ Source: TODAY

Sarah Michelle Gellar is ready to "party" with her pal Shannen Doherty.

The "Cruel Intentions" star took to Instagram on Wednesday to honor Doherty with a touching post on her 46th birthday.

Gellar, 39, poured her heart out in tribute to the "birthday girl," who's been battling breast cancer for more than two years.

"She's everything. She's inspired me...well since... even before I called her a friend," wrote the "Buffy the Vampire Slayer" alum. "But over the last year, I have watched her inspire and give hope to the world."

Gellar, who's repeatedly gushed about Doherty's bravery throughout her ordeal, went on to marvel over her friend's strength.

"I thought I knew how tough she was, but I didn't even have a clue to her power. When I think twice about leaving the house without makeup, Shannen shaved her head on the public stage. While I fiercely guard my privacy, she opened her life, her struggles, her fears and her journey to help people she has never even met," Gellar wrote, adding that Doherty is a "true friend to everyone."

Sarah Michelle Gellar and Shannen Doherty.Diane Freed / Getty Images

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"Shannen also has the greatest laugh in the world, which is why I chose this picture," Gellar concluded. "To the fiercest, most loyal friend I know....let's party like it's your birthday!!! I love you."