Beverly Hills 90210 alum Shannen Doherty's life changed forever when the actress was diagnosed with breast cancer in March 2015.

Doherty has been very open and candid about her fight against the horrible disease. She often used social media, including Instagram, to update her fans on her journey, including everything from her coping mechanisms, to getting a mastectomy, and shaving her head after two rounds of chemotherapy.

"After my second treatment, my hair was really matted, like in dreadlocks. And I went to try and brush it out, and it just fell out," she recalled. "I just remember holding onto huge clumps of my hair in my hands and just running to my mom crying, like, 'My hair, my hair, my hair, my hair.'"

Shannen revealed this morning that she is in the battle of her life. Her cancer has returned and it's even more aggressive. She has stage 4 cancer. It was also reveled that the cancer came back last year, before the death of Luke Perry, but she kept it private until now.

"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," Doherty told ABC News' Amy Robach in an interview that aired Tuesday on " Good Morning America ." "I don't think I've processed it. It's a bitter pill to swallow in a lot of ways."

She was candid in the interview with GMA telling them about how it felt to have the diagnosis and how she is coping with it.

"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 said. "But I would say that my first reaction is always concern about how -- how am I going to tell my mom, my husband."

Shannen had her reasons to reveal the diagnosis today. Her condition will become public this week regardless as part of her lawsuit against State Farm over unpaid claims following damage to her house caused by last year's devastating Wolseley fire.

She said, "I'd rather people hear it from me. I don't want it to be twisted, a court document. I want it to be real and authentic. I want to control the narrative. I want people to know from me."

Shannen is letting this get her down. She plans on using her fame as a platform to make a difference and defend other going through similar experiences.

"I think the thing I want to do the most right now is I want to make an impact," she said. "I want to be remembered for something bigger than just me."

Approximately 1 in 8 women (13%) will be diagnosed with invasive breast cancer in their lifetime and 1 in 39 women will die from breast cancer.