Actress Mary Tyler Moore has reached out to offer support to her former TV co-star Valerie Harper after she was diagnosed with terminal brain cancer.

Harper, who played Moore's best friend Rhoda Morgenstern on The Mary Tyler Moore Show, has been told she has just months to live after developing a rare condition called leptomeningeal carcinomatosis.

Moore, herself, underwent surgery in 2011 for a benign tumour in the membrane surrounding the brain, where Harper's malignant cancer cells are.

Now the 76 year old has reacted to her friend's diagnosis, telling People.com, "I'm absolutely devastated by this news. Valerie has given so much joy, laughter and love to the world. I join her fans and send much love and positive thoughts to her and her family during this difficult time."

Harper insists Moore has been "a great girlfriend" in real life for decades, and she called her old pal up to tell her about her cancer one day before going public with the news on Wednesday.

Harper recalls, "She said, 'What's up?' I said, 'It's incurable cancer.' She said, 'Val, I'm so sorry...' Mary said, 'One day at a time. That's how we've got to live our lives. That's the best we can do.' I love her... I learned so much from her and she shared so much."

Meanwhile, actress Roma Downey who worked with Harper on TV drama Touched By An Angel, has added her thoughts after learning the sad news, saying, "We’re going to keep her in our prayers, I love Valerie, I love working with her, she is a beautiful, wonderful, generous hearted women."