Shannen Doherty's cancer fight has taken a heartbreaking toll on her.
"It's hard," she acknowledges to ET's Jennifer Peros, shedding tears. "I started thinking that I wasn't going to live... I don't look past today."
"I don't know if I'll ever look like me again," she adds, wearing a scarf over her head.
In the emotional sit-down, Doherty reveals a devastating setback in her diagnosis for the first time.
"I want to believe that if I fight, I'm gonna be OK," she says.
Doherty's exclusive interview airs on Monday, only on ET.
On Wednesday, ET chatted with her former Beverly Hills, 90210
co-star, Jason Priestley, who shared his love and well-wishes for his on-screen sister
. Priestley was especially moved by Doherty's decision to share pictures of her shaving her head
"What she did the other day, shaving her head and posting the pictures and everything, that was incredibly brave," Priestley, 46, said. "Shannen's a strong kid and a tough fighter, and I know that she's gonna come through this fight and she's gonna be OK."
Fellow Beverly Hills, 90210 actress Tiffani Thiessen also shared kind words.
"I wish her all the best, of course," Thiessen told ET.