“Good Morning America” anchor Robin Roberts will undergo a bone marrow transplant after being diagnosed with a form of leukemia. On the show this morning, an emotional Roberts explained she was diagnosed with the cancer as a result of treatment she received in 2007 after being diagnosed with breast cancer. A revelation she also shared on “Good Morning America.”

“It is something called MDS… a rare blood disorder,” said Roberts.

“You have heard me say I am abundantly blessed,” Roberts added. “The reason I say that I am blessed is that my big sister (right, with Diane Sawyer) is a virtually perfect match and she is going to be my donor.”

Roberts begins pre-transplant procedures today with the transplant occurring later this summer.

Sadly, Roberts learned of the diagnosis on one of the happiest days in her 10 years with “Good Morning America:” the day the show beat NBC’s “Today” in the ratings for the first time in 16 years.

“I am going to beat this. My doctors say it and my faith says it, too.”

Watch Roberts’ announcement after the jump…