Rona Newton-John, Olivia's Sister, Dies Of Brain Cancer

Olivia Newton-John's older sister, Rona, has died. The 70-year-old model and actress was diagnosed with brain cancer last month.

Olivia revealed Rona passed away on Friday, May 24 in Los Angeles, Calif., in a Facebook post Wednesday.

My beautiful sister Rona sadly passed on May 24th in Los Angeles. It was May 25th in Australia - which was our mother Irene's birthday. Rona died of a very aggressive brain tumor and mercifully suffered no pain. She was surrounded by the love of her four children - Fiona, Brett,Tottie and Emerson and, her wonderful friends. I will miss her forever - my beautiful, smart, talented, funny, brave sister Rona.

In lieu of flowers, the family has asked donations be sent to the Olivia Newton-John Cancer & Wellness Centre . A brain tumor fund will be set up in Rona's memory and the funds will go to helping people battling the disease.

In April, Olivia first announced Rona had been diagnosed with brain cancer . The "Grease" legend decided to postpone her Las Vegas residency to be by her sister's side.

"As a cancer 'thriver' myself , as many people are, I am very aware of the importance of love, support and family during this journey she is about to begin," the 64-year-old, who was diagnosed with breast cancer more than 20 years ago, told "Entertainment Tonight" in a statement. "I want to thank everyone in advance for respecting our privacy during this difficult time."

Rona was a model early in life and then became an actress, appearing on shows like "The Benny Hill Show," "UFO" and "Sordid Lives." She was married to Olivia's "Grease" co-star Jeff Conaway from 1980 to 1985. ABC News reports she had been working on a memoir , titled The Dark Side of Charisma, for several years. It is set to be released this summer.