As Joan Lunden puts it, she "heard those words that every woman fears and never wants to hear."

The former Good Morning America host revealed on the morning show she is battling breast cancer, telling Robin Roberts the diagnosis came as "a shock."

"For me, I'm a health advocate," said the 63-year-old. "I'm all over America talking to women, saying, 'Make sure that you get all of your checkups all the time.' You almost feel like, 'What did I do wrong?'"

The award-winning journalist has since gone "into warrior mode" after finding the lump via an ultrasound and already began chemotherapy as her cancer is the "more aggressive kind."

joan lunden

Joan with daughters [from left] Sarah, Lindsay and Jamie

But she's doing her best to focus on the positives. "Because we found it early, I was able to tell [my children] that mommy's going to be okay," the mom-of-seven [ranging in age from 9 to 33] shared.

In a personal note on her website, Joan wrote, "I have decided to talk about my breast cancer because since the moment I took the job at Good Morning America I have lived my life sharing my joys and my disappointments with all of you: my pregnancies, my relationships, my career."

She continued, "It certainly didn’t feel right keeping this part of my journey a secret."

Co-hosting GMA from 1980 until 1997, Joan is unfortunately not the first in her ABC family to receive a breast cancer diagnosis. Robin battled the disease, as well as myelodysplastic syndrome, in 2007 while Amy Robach recently completed chemo after discovering a tumor last October.

Joan took to Twitter shortly after the announcement, writing: