Robin Roberts signed off from "Good Morning America" Thursday morning, one day before she was expected to start an extended medical leave for treatment of MDS.

"“This is uncharted territory," the 51-year-old anchor said. "We’ve been talking very open about what’s ahead. I had planned for tomorrow to be the last day, but some things happened at home, and I wanna take care of that before I begin treatment next week."

Her treatment includes chemotherapy and a bone marrow transplant from her sister Sally Ann. Robin hopes to return to the morning show as soon as possible, but her oncologist urged her not to put a timetable on her recovery.

"We look at the first 30 days out as the time to rebuild your system." Dr. Gail Roboz said. "The transplant has to figure out to rebuild your immune system and get you well again. You’re getting blood and antibiotics to protect you til you’re up and running again." Watch Robin's final farewell below:

Country star Martina McBride serenaded Robin with her inspirational song, "I'm Gonna Love You Through It." Robin had appeared in the music video for the song alongside fellow cancer survivors Sheryl Crow and Hoda Kotb. Watch her emotional performance below:

A slew of celebrities -- including Oprah Winfrey, Diane Sawyer, Barbara Walters and Katie Couric -- will guest host while Robin is on medical leave.

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