Olivia Newton-John is in mourning after her sister lost her battle with brain cancer.

The singer/actress called off her Las Vegas residency earlier this year (13) following her elder sibling Rona's diagnosis, but the 70 year old has now died, according to the Sydney Morning Herald.

The Grease star, who battled breast cancer in the early 1990s, has yet to comment on her sister's recent passing, but revealed to fans last month (Apr13) that she wanted to spend as much time with Rona as possible.

She stated, "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. I want to thank everyone in advance for respecting our privacy during this difficult time."