Tennis Grand Slam queen Martina Navratilova said she was diagnosed with a non-invasive form of breast cancer, telling People magazine in its Wednesday edition that her prognosis was excellent.

In a candid interview with the U.S. entertainment weekly, Navratilova said she cried when her biopsy came back positive after a routine mammogram in February.

"It knocked me off my ass, really. I feel so in control of my life and my body, and then this comes, and it's completely out of my hands."

The tennis legend's doctor and close friend, Dr. Mindy Nagle, sounded optimistic about Navratilova's prognosis, saying, "It was the best-case scenario you could imagine for detecting breast cancer."

Navratilova had a lumpectomy and was scheduled to begin six weeks of radiation therapy in May.

The 53-year-old athlete admitted to falling behind on regular breast exams and issued a warning for women to stay diligent about frequent check-ups.

"I went four years between mammograms," she told People .

"I let it slide. Everyone gets busy, but don't make excuses. I stay in shape and eat right, and it happened to me. Another year and I could have been in big trouble."