The 48-year-old actress made the announcement to her fans in an interview that aired Tuesday on "Good Morning America."
"It's going to come out in a matter of days or a week that I'm stage 4. So my cancer came back and that's why I'm here," she told Amy Robach.
The "Beverly Hills, 90210" actress added: "I don't think I've processed it. It's a bitter pill to swallow in a lot of ways."
Doherty, who was first diagnosed with breast cancer in 2015 but entered remission following chemo and radiation, opened up about how the recent diagnosis has affected her.
"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," she told Robach. "But I would say that my first reaction is always concern about how -- how am I going to tell my mom, my husband."
In August, Doherty told People magazine she was "lucky to be alive every minute."
According to the outlet, Doherty initially underwent hormone therapy before undergoing a mastectomy, followed by back-to-back rounds of chemo and radiation. Then in 2018, she underwent reconstruction with an innovative surgery called DIEP flap, in which the breast is rebuilt using the patient’s own tissue.
“I really took good care of myself, and I came out of it in as good of condition I think somebody [in my situation] could be in,” said Doherty. “But the funny thing with cancer is that once you’re no longer on chemo or radiation, people think you’re fine, that you bounce back. But what they don’t realize is that your body has been through something so incredibly difficult that your body never fully bounces back.”
Since her initial diagnosis, the "Charmed" actress returned to work on the "90210" reboot in 2019.
Reps for Doherty did not immediately respond to Fox News' request for comment.