By Jessica Wilder

Olivia Newton-John's older sister, Rona Newton-John, who was diagnosed with a brain tumor last month, died May 24 at age 70.

"She was surrounded by the love of her four children-Fiona, Brett, Tottie and Emerson and her wonderful friends," Newton-John wrote on her Facebook page. "I will miss her forever-my beautiful, smart, talented, funny, brave sister Rona."

The 64-year-old actress also battled cancer just 20 years ago and had always been supportive of her sister, postponing a Las Vegas show to be with her in April. "As a cancer thriver, myself… I am aware of the importance of love, support and family during this journey," she said at the time.

Rona, an actress herself, was married to Newton-John's "Grease" co-star Jeff Conaway from 1980 to 1985. She had been working for several years on a memoir, "The Dark Side of Charisma," set for release this summer.

In lieu of flowers the family would appreciate donations to the Olivia Newton John Cancer & Wellness Centre, where a brain tumor wellness program will be started in Rona's name.