Rona Newton-John, the sister of singer-actress Olivia Newton-John, died recently at the age of 70.

Newton-John, who was diagnosed with a brain tumor last month, died on May 24, according to a statement released by Olivia via her Facebook page.

“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,” Olivia wrote.

Olivia Newton-John was diagnosed with breast cancer 20 years ago but has been free of the disease since receiving a mastectomy and undergoing treatment.

Rona Newton-John, who was also an actress, had been working on a memoir called "The Dark Side of Charisma" for  the past few years, ABC News reported. The book is set for release this summer.

The Newton-John family has requested that in lieu of flowers, people send donations to the Olivia Newton-John Cancer & Wellness Center, where a brain tumor wellness program will be started in Rona's name.