"I don't think of dying – I think of being here now, the Rhoda actress, who has as little as three months left, tells PEOPLE

Valerie Harper is facing a devastating diagnosis: terminal brain cancer.

The television icon – beloved for her role as brash New Yorker Rhoda Morgenstern on The Mary Tyler Moore Show and its spin-off, Rhoda – received the news on Jan. 15, she reveals to PEOPLE in this week’s exclusive cover interview.

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A battery of tests revealed she has leptomeningeal carcinomatosis, a rare condition that occurs when cancer cells spread into the fluid-filled membrane surrounding the brain. Her doctors say she has as little as three months left to live.

Resolved to face her last days with courage and humor, “I don’t think of dying,” says the actress, 73, who previously battled lung cancer in 2009. “I think of being here now.”