Nearly three years after entering remission for breast cancer, Shannen Doherty has been diagnosed with Stage 4 cancer. The actress revealed the diagnosis in an interview with ABC News's Amy Robach that aired Tuesday morning on Good Morning America.

"It's going to come out in a matter of days or a week that I have Stage 4," said Doherty, who did not specify her cancer type by name. "So my cancer came back. And that's why I'm here."

"I don't think that I've processed it," Doherty added. "It's a bitter pill to swallow in a lot of ways."

Doherty was first diagnosed with breast cancer in March 2015. She announced her remission two years later. The former star of Beverly Hills, 90210 and Charmed said that her cancer returned prior to the filming of last year's 90210 meta-revival, BH90210, which entered production shortly after her former co-star Luke Perry died unexpectedly following a massive stroke. Doherty admitted to wondering, "Why wasn't it me?" when it came to Perry's death.

"It was so weird for me to be diagnosed and then somebody who was, you know, seemingly healthy to go first," said Doherty, who also appeared in Riverdale's tribute to Perry. "It was really shocking. And the least I could do to honor him was do that show. I still haven't done enough, in my opinion. So it's a hard one."

The actress said she leaned on co-star Brian Austin Green on the set of BH90210, revealing that he was the only person in the cast who was aware of her diagnosis during filming. "I had moments of great anxiety where I thought, 'I can't really do this,' and Brian was the one person who, of that group of people, that knew — that I told pretty quickly," Doherty said.

Doherty also said that she she hoped continuing to work would inspire people in similar situations. "People can look at that and say, 'Oh my god, yeah, she can work, and other people with Stage 4 can work too,'" she explained. "Our life doesn't end the minute we get that diagnosis. We still have some living to do."

Doherty said she chose to reveal that her cancer is back now because she expected the news to come out over the course of her ongoing legal fight against her insurance company, State Farm. The actress sued State Farm after her California home was damaged in the Woolsey Fire in 2018.

"I'd rather people hear it from me," she said of her decision to reveal the diagnosis. "I don't want it to be twisted. I don't want it to be a court document. I want it to be real and authentic, and I want to control the narrative."

Doherty admitted that she's "petrified" by her cancer's return but said she wants to use her life to make an impact. "I want to be remembered for something bigger than just me," she said.