"Sex and the City" star Cynthia Nixon announced Tuesday that she has been diagnosed with breast cancer.

Nixon, 42, revealed the diagnosis while doing promos for ABC's Good Morning America. Nison said she had gone for a "completely routine mammogram" in 2006 when she got a call from her gynecologist.

"I basically told them they found some cancer in my right breast," said Nixon, whose girlfriend is NYC-based activist Christine Marinoni. "It's very small and it's very early."

Nixon said she "made a big point" of telling her two children she had the disease. Nixon raises her children, whom she had with ex-husband Danny Mozes, with her gay partner Marinoni.