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.

In her blog post, Roberts elaborated on her diagnosis:

I received my MDS diagnosis on the very day that Good Morning America finally beat the Today Show for the first time in 16 years. Talk about your highs and lows! Then a few weeks ago, during a rather unpleasant procedure to extract bone marrow for testing, I received word that I would interview President Obama the next day. The combination of landing the biggest interview of my career and having a drill in my back reminds me that God only gives us what we can handle and that it helps to have a good sense of humor when we run smack into the absurdity of life.

Bottom line: I’ve been living with this diagnosis for awhile and will continue to anchor GMA. I love what I do and the people with whom I do it. Along with my faith, family and friends, all of you at ABC News give me the motivation and energy to face this challenge.

In a note to staff, ABC News president Ben Sherwood praised Roberts.

"We love Robin, the heart and soul of ABC News, and we'll stand arm in arm with her as she fights this new battle," he wrote. "She is the captain of our 'GMA' team; she has been the keystone of our recent victories; and she will lead the program for many years to come."

video platform
video management
video solutions
video player

Loading Slideshow...
  • Robin Roberts

  • Michelle Obama

  • GeorgeStephanopoulos

  • Josh Elliott

  • Lara Spencer

  • Jake Tapper

  • Dan Abrams

  • Ali Velshi

  • Bonnie Fuller

  • Keith Olbermann

  • Buster Olney

  • HowardKurtz

  • Nick Schifrin

  • Obama Expresses Support For Same-Sex Marriage During Television Interview

    WASHINGTON, DC - MAY 9: U.S. President Barack Obama participates in an interview with Robin Roberts of ABC's Good Morning America, in the Cabinet Room of the White House on May 9, 2012 in Washington, DC. During the interview, President Obama expressed his support for gay marriage, a first for a U.S. president. (Photo by Pete Souza/White House Photo via Getty Images)

  • 84th Annual Academy Awards - Arrivals

    HOLLYWOOD, CA - FEBRUARY 26: TV personality Robin Roberts arrives at the 84th Annual Academy Awards held at the Hollywood & Highland Center on February 26, 2012 in Hollywood, California. (Photo by Ethan Miller/Getty Images)

  • "Oscar's Red Carpet Live" Hosts Visit "Good Morning America"

    NEW YORK, NY - FEBRUARY 13: (L-R) George Stephanopoulos, Robin Roberts, Tim Gunn, Jess Cagle, Nina Garcia and Louise Roe attend the revealing of the 'Oscar's Red Carpet Live' hosts on 'Good Morning America' at ABC Studios on February 13, 2012 in New York City. (Photo by Janette Pellegrini/Getty Images)

  • "Stick Fly" Broadway Opening Night - Arrivals & Curtain Call

    NEW YORK, NY - DECEMBER 08: Robin Roberts attends the 'Stick Fly' Broadway opening night at the Cort Theatre on December 8, 2011 in New York City. (Photo by Donna Ward/Getty Images)

  • Nicki Minaj Performs On ABC's "Good Morning America"

    NEW YORK, NY - AUGUST 05: ABC's 'Good Morning America' co-host Robin Roberts and singer/rapper Nicki Minaj onstage at ABC's 'Good Morning America' at Rumsey Playfield, Central Park on August 5, 2011 in New York City. (Photo by Jemal Countess/Getty Images)

  • Brad Paisley Performs On ABC's "Good Morning America" - July 15, 2011

    NEW YORK, NY - JULY 15: Broadcaster and co-anchor of ABC's Good Morning America show Robin Roberts (L) and singer/songwriter Brad Paisley speak to the audience on ABC's 'Good Morning America' at Rumsey Playfield, Central Park on July 15, 2011 in New York City. (Photo by Mike Coppola/Getty Images)

  • The Go-Go's Perform On ABC's "Good Morning America" - June 3, 2010

    NEW YORK, NY - JUNE 03: (L-R) Vocalist Belinda Carlisle of the Go-Go's talks with GMA anchors Robin Roberts and Lara Spencer on ABC's 'Good Morning America' at Rumsey Playfield, Central Park on June 3, 2011 in New York City. (Photo by Michael Loccisano/Getty Images)

  • 83rd Annual Academy Awards - Arrivals

    HOLLYWOOD, CA - FEBRUARY 27: TV personality Robin Roberts arrives at the 83rd Annual Academy Awards held at the Kodak Theatre on February 27, 2011 in Hollywood, California. (Photo by Jason Merritt/Getty Images)