Jason Priestley says Shannen Doherty has ''always been a fighter'' as she battles cancer.

The 'Beverly Hills, 90210' star is battling stage four cancer and her former co-star has been incredibly supportive of Shannen and knows she will ''fight''.

Speaking to Australia's Studio 10, he said: ''I reach out to Shannen every few months, just to check in on her and say hi. Shannen's a real tough girl, and Shannen's a fighter and she's always been a fighter and I know that she will continue to fight as hard as she can.''

Meanwhile, Jason previously admitted he was ''heartbroken'' over Shannen's cancer diagnosis.

The 50-year-old actor said: ''I reached out to her yesterday when the news broke. She's overwhelmed with well wishers and with people reaching out to her. I haven't heard back from her yet, but I'm sure that I will very soon. Shannen was a big part of my life. Shannen and I will always have a bond that is very meaningful. I'm very heartbroken about the news and I wish her and her family the best in this very difficult time.''

Shannen revealed her diagnosis this week, when she admitted she's still struggling to ''process'' the news.

The 48-year-old actress 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. And that's why I'm here. 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 - how am I going to tell my mom, my husband.''