The two stars played teenage sweethearts Danny Zuko and Sandy Olsson in the hit film adaptation of the musical, performing together on songs like Summer Nights, You’re The One That I Want and We Go Together.
After the news broke on Monday evening that Olivia had died, John was among those to pay tribute to his friend and former colleague.
“My dearest Olivia,” he wrote, alongside a vintage snap of the Physical singer. “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!”
He signed off his tribute: “Your Danny, your John!”
Olivia’s husband John Easterling announced the news of her death on Facebook, writing: “Dame Olivia Newton-John (73) passed away peacefully at her Ranch in Southern California this morning, surrounded by family and friends.
“We ask that everyone please respect the family’s privacy during this very difficult time.”
The British-born, Australian-raised star was diagnosed with breast cancer for the third time in 2017, after she was previously cured of the disease in 1992 and 2013.
Olivia’s husband added: “Olivia has been a symbol of triumphs and hope for over 30 years sharing her journey with breast cancer.
“Her healing inspiration and pioneering experience with plant medicine continues with the Olivia Newton-John Foundation Fund, dedicated to researching plant medicine and cancer.”
As well as her work in Grease, Olivia had a long career in the music industry, with hits including Physical, Twist Of Fate and I Honestly Love You, which was awarded Record Of The Year at the Grammys.
Following the mammoth success of Grease, which remains popular to this day, she also appeared in the film Xanadu, teaming up with the Electric Light Orchestra on the accompanying soundtrack.
More than 30 years after sharing the screen in Grease, Olivia reunited with John Travolta for the festive album This Christmas in 2012.
In addition to her music and acting career, Olivia was also known for her activism for animal rights and the environment, as well as raising awareness of breast cancer.
In 2020, she was given a damehood in the for services to charity, cancer research and entertainment in the Queen’s New Year Honours.
She is survived by her husband John and daughter Chloe, whose father is Olivia’s first husband, the actor and dancer Matt Lattanzi.