Image credit: @MichelleObama

First Lady Michelle Obama has a special message for ABC News' Robin Roberts, who announced today that she is battling a rare blood disorder.

"@RobinRoberts, Barack and I have you in our prayers. We believe in you and thank you for bringing awareness and hope to others," the First Lady tweeted.

The post was signed "-mo" to note that Mrs. Obama tweeted it herself.

The "Good Morning America" co-anchor who beat breast cancer five years ago has been diagnosed with myelodysplastic syndrome, a blood disorder that affects the bone marrow.

Read Robin Roberts' letter about her diagnosis with MDS.