Olivia Newton-John
Olivia Newton-John has announced the death of her older sister, Rona.

Olivia Newton-John is in mourning following the death of her older sister.

The Grease star, herself a breast cancer survivor, told fans of her grief after Rona lost her battle with brain cancer.

Announcing her sister's passing on her Facebook page she paid tribute to her 'brave sister'.

"She was surrounded by the love of her four children -- Fiona, Brett, Tottie and Emerson and her wonderful friends," she wrote.

"I will miss her forever -- my beautiful, smart, talented, funny, brave sister Rona."

In April, the 64-year-old singer and actress, postponed a string of performances to spend time with her family as they came to terms with her sibling's diagnosis.

She had been due to start a residency in Las Vegas with a regular show at the Flamingo hotel.

"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," Newton-John told fans at the time.

Rona, a former model and actress, appeared on shows including the The Benny Hill Show. She was also married to Newton-John's "Grease" co-star Jeff Conaway from 1980 1985.

Her memoir, "The Dark Side of Charisma," is to be published this summer.