After a double mastectomy, Good Morning America news anchor Amy Robach is now in good health and chronicling her cancer fight in her book, Better. She opened up to ET about her darkest days.

"It was the worst possible moment of my life," Robach, 42, told ET about her diagnosis. "It was the most scared I have ever been in my life."

MORE: ABC News' Amy Robach Diagnosed with Breast Cancer

Robach's first mammogram happened live on GMA in October 2013 for Breast Cancer Awareness Month at the urging of friend and cancer survivor Robin Roberts. The following month, Robach announced on GMA that she had been diagnosed with breast cancer.

"The whole time I was sitting there contemplating not having that mammogram, I had two malignant tumors in me and the cancer had already spread to my lymph nodes," Robach said.

Robach went through a double mastectomy and eight rounds of chemotherapy to get back to good health, all while appearing on GMA and raising a family (she has two daughters, Annie and Ava, with ex-husband Tim McIntosh, and a stepson, Nathaniel, with husband Andrew Shue).

WATCH: Robin Roberts on Disease Fight: At One Point I Wanted to Die

"I think for me going through this disease, the most beautiful part was how kind everyone was to me," Robach said, fighting back tears. "And just the smallest acts of kindness had such a huge impact, like an email, a letter, a hug. It was everything to me, and I now with my daughters before they go to bed at night, I say, 'Who were you kind to today, and who will you be kind to tomorrow?'"

In Better, available now, Robach recounts with honesty and humor, the difficulty of breaking the news of her diagnosis to her two young daughters and the challenges of carrying on with her life through her battle against breast cancer. She also imparts wisdom about what it means to endure and to come out of a struggle better than before.