By Derek Lawrence
Updated August 09, 2016 at 07:53 PM EDT
Credit: sarahmgellar/Instagram

On Monday, Sarah Michelle Gellar shared an emotional Instagram post dedicated to her friend, Shannen Doherty, who is currently battling breast cancer.

Gellar posted a photo of her alongside the Beverly Hills, 90210 alum, and wrote, “My #mondaymuse (and really every day #muse) is my brave friend @theshando, 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 #F—Cancer.”

Doherty was originally diagnosed in March 2015, and last week in an emotional sitdown interview with Entertainment Tonight, she revealed that her cancer has spread. “The unknown is always the scariest part,” she said. “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?”

Watch a clip of Doherty’s interview below.