Robin Roberts' news shakes 'GMA' crew

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NEW YORK -- The mood on the set of ABC’s “Good Morning America” seemed somber at 6:45 this morning.

The control room wasn’t showing signs of controlled chaos for the live national show from 7 a.m. to 9 a.m. The production assistants weren’t laughing and talking about their weekend. The anchors were quietly reading their scripts and preparing for the show.

Something was different.

Then Diane Sawyer walked in.

The anchor of ABC News’ flagship nighttime program, "World News With Diane Sawyer," and former 10-year cohost of “Good Morning America,” was in the studio at 6:45 a.m. to support her friend, Robin Roberts, who would wait two hours to announce her news to the world.

The “GMA” crew would close the set around 8:45 a.m. to allow Roberts, who had beaten breast cancer for five years, to announce on the air that she has been diagnosed with myelodysplastic syndrome, a disease of the blood and bone marrow that was once known as preleukemia. She had known since earlier this spring, but had kept the news quiet except for telling her closest friends.

“My doctors tell me I’m going to beat this –- and I know it’s true,” Roberts said.

Her co-workers – George Stephanopoulos, Josh Elliott, Sam Champion and Lara Spencer -– all said a few words and shed a few tears.

Sawyer was there to offer support, and so was Sally-Ann Roberts, who is donating bone marrow cells to Robin, her younger sister.

After the live show, the cast and crew hugged and wished Roberts well.

Elliott, who previously worked at ESPN, said it best: “Robin, this isn’t just your fight. It’s our fight.”

Here's Roberts' statement; the reaction on Twitter has been swift: