ABC correspondent and anchor Amy Robach -- who underwent a double mastectomy for advanced breast cancer three weeks ago -- returned to "Good Morning America" Thursday, telling viewers that "I feel remarkably well. Mentally, it's another challenge because that was phase one."

Robach also said she would continue to work while undergoing chemotherapy. Her treatment begins Dec. 16 and will continue for four months, she said.

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Robach, 40, discovered her cancer after undergoing an on-air mammogram in October to launch "GMA's" coverage of Breast Cancer Awareness Month. She later said that during surgery her doctor had found another previously undetected malignancy and that it had spread to a sentinel lymph node.

"It forces you to live in the moment," she said of her surgery and recovery. "I think that's a good lesson for everyone. If you look at the positive out of this, there are days if you let your mind wander, it's fairly devastating."