Gellar, 39, paid tribute to Doherty, 45, in a Monday Muse post on Instagram following news the Charmed star’s breast cancer has spread.
“My #mondaymuse (and really every day #muse) is my brave friend @theshando,” Gellar captioned a photo of herself with the actress.
“I’ve always said she is one of the most loyal friends I’ve ever known, and now while she is facing the toughest journey of her life, she is sharing it with friends she has never met in the hopes of helping other people who are going through the same struggle. That’s a true friend,” she added.
“The unknown is always the scariest part,” she told Entertainment Tonight on Aug. 1. “Is the chemo going to work? Is the radiation going to work? You know, am I going to have to go through this again, or am I going to get secondary cancer?”
“Everything else is manageable,” the star said. “Pain is manageable, you know, living without a breast is manageable — it’s the worry of your future and how your future is going to affect the people that you love.”
Doherty, who married photographer Kurt Iswarienko in 2011, is best known for Charmed and Beverly Hills, 90210. Gellar, meanwhile, starred on Buffy the Vampire Slayer and will appear in NBC’s Cruel Intentions pilot.