Robin Roberts MDS: 'GMA' Co-Host Announces She Has Bone Marrow Disease

An emotional Robin Roberts announced on Monday that she has been diagnosed with a rare blood and bone-marrow disorder called MDS, and will undergo a bone marrow transplant.

Speaking on "Good Morning America" and writing on a blog post, Roberts said the disease was once called preleukemia, and is a complication from the treatment she received to beat breast cancer in 2007.

On the "GMA" website, Roberts wrote that, while there are some "scary" statistics about the disease, her doctors have told her she is young and fit enough to beat it.

Roberts made the announcement toward the end of Monday's "GMA," surrounded by her co-hosts and with former co-host Diane Sawyer (whom she called "my Thelma") in attendance.

"Sometimes treatment for cancer can lead to other serious medical issues and that's what I'm facing right now," she said. "The reason I am sharing this with everybody right now is because later today I begin what's known as pre-treatment."

Roberts said that a tube was being added to her arm Monday afternoon. "I didn't want you to be concerned if you saw a bandage tomorrow,” she said. "It's going to be there to draw blood ... and also to administer drugs."

She said that she will be "out for a chunk of time" after she receives a bone marrow transplant from her sister, who doctors said was a "perfect match" for her.

She pledged to overcome the disease.

"I'm going to beat this," she said, choking up. "My doctors say it and my faith says it to me." She received a round of applause at the end of her comments.