Sandra Lee, a popular TV chef and author, revealed on Good Morning America today in an emotional interview that she was diagnosed with breast cancer.

Lee, 48, said she got the news via a phone call from her doctor while she was on set with People magazine for their "Most Beautiful" issue on March 27.

"And I walked off the set, and 20 minutes later my doctor called and told me I had breast cancer," Lee told GMA co-anchor Robin Roberts, who is also a breast cancer survivor. "I didn't even cry, I was stunned ... You know, and that's just how fast life turns. It turns on a dime."

Lee told Roberts that she is taking her doctor's advice and will undergo a double mastectomy.

Despite the bad news, Lee isn't letting her diagnosis ruin her life.

"It beats up your body, and it beats you up emotionally. And it -- I wasn't going let it rob me from one day of happiness," Lee said in the interview.

Lee is telling her story to encourage women to start getting mamograms earlier in life. Today she urged women to get them now on GMA and on her Facebook page.

Some organizations recommend getting mammograms beginning at age 40, while others recommend waiting until 50.

Lee said that waiting until 50 is too late, using the example that she was diagnosed at age 48 and Roberts was diagnosed at age 46.

"Girls in 20s and their 30s just have to know. And I don't want women to wait. And that's why I'm talking ... If it saves one person, and makes one more person go get a mammogram, and if they're sitting down right now watching this, don't watch this TV. Go pick your phone up, and call your doctor and get your rear end in there and get a mammogram right now," Lee said in the interview.

Watch the interview here.