Shannen Doherty has revealed her cancer has returned and said it is a "bitter pill".
The Beverly Hills 90210 actress was first diagnosed with breast cancer in March 2015 but had gone into remission.
However, the 48-year-old told US breakfast show Good Morning America that the cancer had returned a year ago.
"It's going to come out in a matter of days or a week that I'm stage four," she said.
"So my cancer came back and that's why I'm here."
Doherty said she had kept the news out of the public domain for a year, adding: "I don't think I've processed it. It's a bitter pill to swallow in a lot of ways.
"I definitely have days where I say, 'Why me?' And then I go 'Well, why not me? Who else? Who else besides me deserves this? None of us do'.
"But I would say that my first reaction is always concern about how am I going to tell my mom, my husband."
Doherty kept the news to herself and went back to work on the reboot of the show, almost four months after the death of former co-star Luke Perry.
"It's so weird for me to be diag- nosed and then somebody who was seemingly healthy to go first," she said.
"It was really shocking. And the least I could do to honour him was to do that show. I still haven't done enough, in my opinion. So it's a hard one.
"One of the reasons, along with Luke, that I did 90210 and didn't really tell anybody because I thought, people can look at that, other people with stage four can work too. Like our life doesn't end the minute we get that diagnosis."
To make it through filming, Doherty said she leaned on co-star Brian Austin Green after telling him the news.
"Prior to shooting, he would always call me and say, 'Listen, you know, whatever happens, I have your back'," she said.