The 63 year-old's type of cancer is "aggressive," and she will have to undergo chemotherapy, surgery and radiation treatment.
Joan Lunden revealed that she had recently been diagnosed with breast cancer.
The announcement came on Tuesday morning (June 24th) when the 63 year-old returned to 'Good Morning America.'
Lunden spoke candidly of her experience on hearing the diagnosis to 'GMA' co-host Robin Roberts, who, along with fellow news anchor Amy Robach, has suffered from the disease.
"I heard those words that every woman fears and never wants to hear, 'You have breast cancer,'" she bravely said.
The journalist and author stated that the cancer wasn't found in her annual mammogram, but in an ultrasound that was performed after, which is usual because she has "dense fibrous tissue."
"Nothing showed in my mammogram and you come out of there like, 'Yes, one more year. I'm okay,'" Lunden continued. "And then you go all happy-go-lucky into the ultrasound and she kept going back to one spot."
Due to her breast cancer being "aggressive," Lunden's treatment will consist of chemotherapy, surgery and radiation, but she is likely to make a full recovery.
"I've got that journey ahead," she said. "I've already started it. I'm already doing my chemo."
The mother of seven, who hosted 'GMA' from 1980-1997, also took to her own website to open up about reacting to the diagnosis.
"I sat there stunned - how could this be? I considered myself fit and healthy, I get checked faithfully every year and I didn't have a history of breast cancer in my family," Lunden wrote. "But of course after covering many stories about breast cancer over the years, I knew that none of us are exempt. I also knew that I had to jump into action quickly, put together a team, and find the best course of treatment for the kind of cancer that I have."
She also took this opportunity to explain her reasons for publically speaking about fighting the disease.
"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. I have shared my journey," she wrote. "So it certainly didn't feel right keeping this part of my journey a secret."
Lunden opened up about her diagnosis on Tuesday's 'GMA' edition