Former 'GMA' Host Joan Lunden Diagnosed with Breast Cancer

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Former Good Morning America host Joan Lunden revealed on the ABC morning show Tuesday that she has been diagnosed with breast cancer.

Lunden, 63, revealed the news to Robin Roberts.

Related: Robin Roberts -- I Felt I Was Dying

"I knew the minute the doctor came in the door. I could tell by her demeanor. 'You have breast cancer.' The words are so surreal," she told Roberts.

Lunden's treatment will include a lumpectomy, chemotherapy and radiation, but she is expected to make a full recovery.

"I have covered many stories about breast cancer over the years but I never actually thought this would happen to me," Lunden said in a statement. "I have shaped my career around health & wellness advocacy so it seemed natural to share my story. I've started chemotherapy and while I don't know how I’ll look and feel down the road, I am assuming the best because that is how I live my life."

She also tweeted her thanks to for the swift support she's already received..

Related: ABC News' Amy Robach Diagnosed with Breast Cancer

Lunden was the longest running host of Good Morning America, co-hosting for nearly 17 years starting in 1976, most memorably alongside Charles Gibson, 71.