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"Entertainment Tonight" has exclusively learned that Natalie Cole has been hospitalized in New York. A close family source tells ET, "She's had a setback and has gone into the hospital."

Our source adds: "The side effects of [Natalie's] treatment and her extensive promotional schedule in support of her just-released new album, Still Unforgettable, led to the Grammy winner's hospitalization."

Just last week, Natalie came to the ET set to talk about her battle with hepatitis C, saying, "This is a virus that was dormant in my body for 25 years. I had no symptoms, was feeling great, working out like a crazy person -- and this just keeled me over, like a feather."

At the time of our interview, she was still being treated for the disease.

"What I have is treated with chemo ... every week," she says, adding that she experiences the traditional side effects from the treatment, such as nausea and her hair falling out.

In the days ahead, Natalie will be able to return home to begin her "month-long bed rest," the singer's reps tell People magazine.

Natalie checked into the NYC hospital last Friday, adds Us magazine.

"She was doing press in New York last week when she got really sick due to chemotherapy she was undergoing to treat her hepatitis," the mag's source says. "She got anemia from the treatment."