Breast Cancer Warriors Robin & Amy Rally ’Round Brave Joan Lunden!

Gutsy breast cancer survivors ROBIN ROBERTS & AMY ROBACH have rallied to help ex-“Good Morning America” host JOAN LUNDEN as she battles the same disease.

Joan, 63, was diagnosed with an aggressive form of breast cancer in mid- June and “agonized over whether to make her condition public,” a friend told The National ENQUIRER.

“But personal calls to (current ‘GMA’ host) Robin and (news anchor) Amy convinced her to go on the air with her story.”

Joan, “GMA” co-host from 1980 to 1997, shared her devastating news on the popular ABC morning show on June 24.

“Now Robin and Amy have become her big sisters,” said the source. “They promised Joan they’ll be there for her every step of the way.”

Robin, 53, battled breast cancer in 2008 with chemotherapy and radiation treatments. Amy, 41, was diagnosed after an on-air mammogram late last year, and completed 20 weeks of chemotherapy in April.

“Joan and Robin are old friends,” added the source. “Robin was one of the first people outside her family who Joan told.”

Joan has already started chemotherapy for the tumor in her right breast, and will soon undergo a lumpectomy to remove it, followed by radiation, sources say.

Sharing the news with her children was “heartbreaking” for Joan, said the source.

“Joan did her best to assure them that mom is going to be okay,” the friend added. They’re rallying around her, said the source.

“Joan knows that Robin and Amy are there for her too. She’s not alone in her fight.”