She told fans she was “in the final stages of recovery” following the procedure and “ready to start the next chapter”.
Anastacia, 45, cancelled her European tour in February after the second diagnosis.
She made a full recovery in 2003 after being treated with surgery and radiotherapy.
Anastacia, famous for her hit single, I’m Outta Love, cancelled 13 dates in April across Europe to promote her latest album It’s A Man’s World.
“In light of Breast Cancer Awareness Month I wanted to take the opportunity to support a cause particularly close to my heart,” she said.
“I was diagnosed with breast cancer for the second time earlier this year and am currently in the final stages of recovery after undergoing a double mastectomy.
“It has been an intense journey but I am feeling great and ready to start the next chapter.
“Breast Cancer Awareness Month gives all who are facing this disease a chance to gain strength and support from each other.
“Early detection has saved my life twice. I will continue to battle and lend my voice in any way I can,” she added.
Angelina Jolie revealed earlier this year that she had undergone a preventative double mastectomy to reduce her risk of developing breast cancer.
Sharon Osbourne also revealed in November that she had undergone a double mastectomy.
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