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US actress Shannen Doherty has revealed she was diagnosed with stage four breast cancer last year.

The Charmed and BH90210 star was first diagnosed with cancer in 2015, but two years later said she was "done with chemo" and feeling "great".

However, speaking on ABC's Good Morning American on Tuesday, the 48-year-old said: "It's going to come out in a matter of days or a week that I'm stage four.

"So my cancer came back."

She added: "I'd rather people hear it from me."

Doherty, who starred as Brenda Walsh in the original Beverly Hills, 90210, has openly documented her battle with cancer on social media - posting videos of herself exercising alongside the hashtag #cancerslayer.

During the filming of last year's reboot though, which came just months after the death of her former co-star Luke Perry, she kept the news of her latest diagnosis to herself and tried her best to "honour" him.

"It's so weird for me to be diagnosed and then somebody who was seemingly healthy to go first," said Doherty.

"It was really shocking. And the least I could do to honour him was to do that show."

'We got this, kiddo'

She admitted she kept the diagnosis largely to herself, to prove that she was still able to work, and only told co-star Brian Austin Green. The actor, who played David Silver, helped her to get through long days of 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 and said, 'Here, this is what I'm dealing with,'" she said.

"So prior to shooting he would always call me and say, 'Listen, you know, whatever happens, I have your back.' He would look at me and be like, 'We got this, kiddo'... so Brian helped me through a lot."

Doherty went on to tell ABC News' Amy Robach she didn't think she'd properly "processed" the news yet and that "it's a bitter pill to swallow in a lot of ways".

"I definitely have days where I say, 'Why me?'" she said. "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."

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