By Daily Mail Reporter

PUBLISHED: 07:58 EST, 28 June 2012 | UPDATED: 08:44 EST, 28 June 2012

Robin Roberts' older sister has spoken out about being her sole bone marrow donor after learning she was a match.

Sally-Ann, who anchors a morning show in New Orleans, will be essential to her GMA host sister's treatments for myelodysplastic syndrome (MDS), a blood and bone marrow disease.

The mother-of-three, 55, told the New York Post yesterday how she had been so desperate to be a match for her sister, she and her friends made a prayer circle around the test kit.

'We prayed, "please let this be a match,"' she admitted.

Perfect match: Sally-Ann Roberts, pictured with Robin earlier this month, has spoken about how she learned she would be her sister's sole bone marrow donor

She admitted: 'Im the big sister. Im the one whos supposed to be suffering because of age. But thats not the way it is.'

To donate her bone marrow, Sally-Ann explained that she will have five days of injections to boost her blood cell count, before her blood is passed through a machine that will extract the stem cells her sister, 51, so desperately needs.

'The way it is explained to me is that they will first have to knock out her immune system in order for my stem cells to be accepted by her body,' she said.

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'We prayed that I'd be a match': Robin Roberts' sister Sally-Ann on learning she was the sole bone marrow donor