Shannen Doherty, who has been battling breast cancer for a year-and-a-half, said that the disease has spread despite undergoing a single mastectomy this past May.

'I had breast cancer that spread to the lymph nodes, and from one of my surgeries we discovered that some of the cancer cells might have actually gone out of the lymph nodes; so for that reason, we are doing chemo, and then after chemo, I'll do radiation,' the 45-year-old told Entertainment Tonight Monday.

The actress, who shot to fame playing Brenda Walsh on the Nineties hit series Beverly Hills, 90210, credited the doctor who performed the mastectomy on her about three months ago, explaining the measures the physician took to make sure she was comfortable with her body after the critical operation.

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Tragic times: Actress Shannen Doherty, 45, revealed to Entertainment Tonight Monday that her breast cancer has spread despite undergoing a single mastectomy in May

Sharing her journey: The Beverly Hills, 90210 star said her experience shopping for a new bra following the mastectomy was 'traumatic and horrible'

'He didn't want me to wake up with absolutely nothing,' the Charmed star told ET. 'It was very important to him that I didn't have that experience, and so he put an expander in so I have a tiny something there. It's cute and sometimes we fill it up and make it bigger and sometimes we reduce it.'

Doherty, who was initially diagnosed with breast cancer in February 2015, continued, 'I'm being so personal right now, but I think a lot of women can probably go, "Yeah, I've been through that." It's great though, you get to pick out what size you want.'

Doherty, who also had roles in the cult classics films Mallrats and Heathers, recalled an emotional memory about being fitted for a new bra in the wake of her May mastectomy.

Emotional confession: Shannen said that while the pain and loss of a breast is 'manageable,' she's worried about how her cancer battle will impact her family and friends

Fighting the good fight: The actress last month shared a series of images on Instagram, revealing she'd shaved her trademark brunette mane amid ongoing chemotherapy

Support network: The Heathers star has been uplifted by friends and loved ones during her health crisis

'It was traumatic and horrible and I didn't think anything of it at the time, then my mom went with me and I broke down crying in the dressing room and ran out. And then sat in the car crying,' the actress told ET.

The Hollywood beauty, who shaved her head after losing hair as part of her ongoing chemotherapy, said that 'the scariest part' of the process is 'the unknown' of what's coming next in her battle with the deadly disease.

'Is the chemo going to work? Is the radiation going to work?' she asked. 'You know, am I going to have to go through this again, or am I going to get secondary cancer?'

Lean on me: Doherty shares a loving glance with her husband Kurt Iswarienko

Shannen, who's been married to photographer Kurt Iswarienko since October of 2011, said that 'everything else' in her cancer battle 'is manageable' - including the pain and 'living without a breast' - but she admittedly worries about her future, and how it's 'going to affect' her loved ones.

Last week, Shannen's former 90210 co-star Jason Priestley, 46, called her 'incredibly brave' for sharing images of her shaved head on social media, and predicted a happy ending for his one-time TV sibling, calling her 'a strong kid and a tough fighter.

'I know that she's gonna come through this fight and she's gonna be OK,' he told ET.