Openly lesbian tennis legend Martina Navratilova says she has breast cancer, the AP reported.

Doctors found a non-invasive cancer during a routine mammogram in January. Navratilova's prognosis is excellent – her type of cancer has a low fatality rate (less than 1%).

She had a lumpectomy and will begin six weeks of radiation therapy in May.

“I cried,” Navratilova said during a Good Morning America interview. “I could not believe it. I thought I was so healthy.”

The 53-year-old Navratilova dominated the women's tennis circuit for more than a decade, racking up 18 Grand Slam wins and a record 9 women's single titles at Wimbledon.

Navratilova fled her native Czechoslovakia and was granted political asylum in the United States at the age of 18.

She's also an avid gay rights advocate. In 2000, the Human Rights Campaign, the nation's largest gay rights advocate, honored Navratilova with their National Equality Award, the group's highest honor.

Navratilova, who announced she was gay in 1981, is among only a handful of openly gay sports figures.