Martina Navratilova Fighting Breast Cancer

April 7, 2010— -- Martina Navratilova has been diagnosed with breast cancer, she announced on "Good Morning America" today.

The day she received her diagnosis was her "personal 9/11," Navratilova told "GMA" anchor Robin Roberts. "I was devastated."

In February, the tennis legend was diagnosed with an aggressive form of ductal carcinoma in situ (DCIS), considered the earliest form of breast cancer. Navratilova said she had a lumpectomy three weeks ago, during which her doctors determined that the cancer had not spread to her lymph nodes.

She says there is only a "very small chance of it coming back."

"It is just in that one breast," she said. "I'm okay and I'll make a full recovery."

As part of her treatment, she will undergo six weeks of radiation in May. Navratilova says she's feeling physically well but has difficult days emotionally, especially when it comes to talking about the diagnosis, which came as a shock.

"I'm this healthy person, I've been healthy all my life, and all of a sudden I have cancer, are you kidding me?" she said.

Navratilova's cancer was diagnosed during a routine mammogram, after not having one for four years, and she hopes that speaking out will inspire other women to get mammograms.

"The reason I wanted to speak about this is to encourage these woman to have mammograms," she said. "I just want to encourage women to have that yearly check-up."

She was feeling healthy at the time of her diagnosis.

"I was feeling absolutely 100 percent fine," she said.

Navratilova will be hosting a live Web chat on Thursday, April 8, 2010 at 1 p.m. on the AARP Web site. CLICK HERE to learn more and register to participate.