'Grease' star Olivia Newton-John dies aged 73

Singer Olivia Newton-John, who gained worldwide fame as the high school sweetheart Sandy in the hit movie Grease, died on Monday after a 30-year battle with cancer. She was 73.

Newton-John "passed away peacefully at her ranch in Southern California this morning, surrounded by family and friends," said a statement from her husband John Easterling posted on her official social media accounts.

The entertainer, whose career spanned more than five decades, devoted much of her time and celebrity to charities after first being diagnosed with breast cancer in 1992.

The British-born and Australian-raised star dedicated a number of albums and concerts to raise funds for research and early detection of the disease, including the construction of a health centre named after her in her adopted home Melbourne.

"I don't like to say 'battled'," a defiant Newton-John told Australia's Channel Seven TV in September 2018 after revealing she had been diagnosed with cancer for a third time.

"I like to say 'win over', because 'battled' sets up this anger and inflammation that you don't want."

'You're the one I want'

Newton-John is best-known for starring in the 1978 musical Grease alongside John Travolta, as the-girl-next-door Sandy, who trades her ankle-length skirt and prim and proper hair for skin-tight black pants and a perm.

The high school sweetheart-turned-bad girl resonated with audiences worldwide, and continues to capture hearts decades after the movie was released.

"Making it was fun but you never know with movies if audiences are going to go with it or not, even if you love it," she said in a Forbes interview in 2018.

"It is incredible that it is still going but it's not even just that, it's showing no signs of stopping. You say 'Sandy and Danny' and people instantly know what you're talking about."

Grease remained the highest-grossing musical for three decades, with Newton-John and Travolta maintaining a close relationship long after the film was made.

Upon hearing about her demise, Travolta took to his Instagram to pen a note to his "favourite" co-star.

"My dearest Olivia, you made all of our lives so much better. Your impact was incredible. I love you so much. We will see you down the road and we will all be together again. Yours from the first moment I saw you and forever!" read the caption. He signed off the post with, "Your Danny, your John!"

"She was my favourite thing about doing Grease," Travolta said in an interview to mark the film's 40 anniversary in 2018.

There was no one else "in the universe" who could play Sandy, he said of Newton-John, who turned 29 during the making of Grease and later revealed she had to be convinced by Travolta to take up the role after self-doubts that she was too old to play a teenager.

"If you were a young man in the 70s..., if you remember that album cover with Olivia with that blue shirt on, with those big blue eyes staring at you," Travolta recalled.

"Every boy's, every man's dream was: 'oh I would love for that girl to be my girlfriend'."

Her career would span from singer and actor, to author and philanthropist in the coming decades, with her passion for cancer research at the forefront, championing natural therapies, including medicinal cannabis in the treatment of cancer.

She performed into her late 60s, until her latest diagnosis, including a two-year residency in Vegas, a 2015 tour with Australian music legend John Farnham and even recording a Club Dance track at 67 with her daughter Chloe Lattanzi.

"I have done everything, and the icing on the cake as well," she said, reflecting on her career. "So I feel grateful for anything that happens now."