"My beautiful sister Rona sadly passed on May 24th in Los Angeles," Olivia wrote on her Facebook. "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."
Rona, who's six years older than Olivia, 64, was also an actress. Olivia suffered her own cancer battle -- breast cancer -- in the early 1990s. She has since been free of the disease after undergoing treatment and a mastectomy.
Olivia, who postponed her Las Vegas residency at the Flamingo hotel to be with her family when Rona was first diagnosed, announced plans to start a brain tumor wellness program to honor her beloved sister.
"In lieu of flowers the family would appreciate donations to the ONJCWC where a brain tumor wellness program will be started in her name," Olivia wrote. "Thank you all for your kind words of love and support."