Travolta, 68, shared a picture of himself and Dame Olivia together in hit film Grease on Instagram and captioned the image: "Happy Birthday my Olivia."
Dame Olivia rose to fame after starring as Sandra Dee in the hit 1978 musical, opposite Travola as Danny Zukko.
She died at the age of 73 after a long battle with breast cancer.
Her husband John Easterling announced the news via her official Facebook page.
He wrote: "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
"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. In lieu of flowers, the family asks that any donations be made in her memory to the Olivia Newton-John Foundation Fund (ONJFoundationFund.org)."
Travolta said at the time: "My dearest Olivia, you made all of our lives so much better," Travolta wrote beside a gorgeous vintage photo of John. "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!Your Danny, your John!"
Dame Olivia is survived by Easterling and her daughter Chloe Lattanzi.
As well as her starring role in Grease she is also most remembered for her pop career, including hit single Physical.
She went public with her first cancer diagnosis, for breast cancer, in 1992.
She had a second bout with cancer in 2013, in her shoulder, but didn’t share it publicly. Then in May 2017, she announced in an interview on Australian television that she had a tumour at the base of her spine.
In 2019 she told 60 Minutes Australia: "If somebody tells you, you have six months to live, very possibly you will because you believe that. So for me, psychologically, it’s better not to have any idea of what they expect or what the last person that has what you have lived, so I don’t, I don’t tune in.”
Watch: Dame Olivia Newton-John died aged 73 in August