Olivia Newton-John's older sister Rona died on May 24 in Los Angeles from cancer.
She was 70 years old.
"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 on her Facebook page Wednesday.
In April, the Grease star reported to Entertainment Tonight that her model and actress sister was diagnosed with brain cancer. Upon finding out about her sister's diagnosis, the 64-year-old actress postponed her own gig at the Flamingo in Las Vegas as a substitute for the Donny & Marie Osmond show, according to Las Vegas Sun.
Rona payed in several TV shows during the '60s and '70s including UFO, The Adventurer and The Benny Hill Show.
"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," said Olivia.
Olivia beat breast cancer in the early '90s. She thanked everyone in advance for respecting her privacy during this difficult time.
Olivia's Wednesday Facebook post also asked that instead of flowers, people donate to the Olivia Newton-John Cancer & Wellness Centre, a brain tumor wellness program that has been initiated for her sister.