Olivia Newton-John, best known for her role as Sandy in Grease, has passed away at the age of 73.

The sad news was announced on Newton-John's Instagram via her husband, John Easterling.

The caption read, "Dame Olivia Newton-John, 73, passed away peacefully this morning at her ranch in Southern California surrounded by family and friends. Please respect the family's privacy during this very difficult time."

"Olivia was a symbol of triumph and hope who shared her journey with breast cancer for over 30 years. Her healing inspiration and pioneering experience with phytotherapy continues with the Olivia Newton John Foundation, dedicated to phytotherapy and cancer research. In lieu of flowers, the family asks that donations be made in her memory to the @onjfoundation."

Tributes soon began pouring in from Newton-John's friends and collaborators.

Her "Grease" co-star John Travolta wrote on Instagram, "My dear Olivia, you have made our entire lives so much better. Your influence on us was unbelievable. I love you so much. See you again down the road. From the first time I saw you and forever!

"Your Danny, your John!"

Fellow singer Mariah Carey shared a lovely story on Twitter: "I dressed up as Bad Sandy for Halloween in 5th grade and thought I was everything. A few years later, THE Olivia Newton John came out on stage with me in Melbourne, Australia and we sang our hearts out together in 'Hopelessly Devoted To You. This is a moment I will never forget."

Actress and producer Viola Davis said, "Oh dear! You were my childhood! Your talent, your poise, your beauty! Rest in glorious peace. God bless your family ...... And thank you for creating memories that will last forever."

Singer Kylie Minogue said, "I have loved and admired Olivia Newton-John since I was 10 years old. And always will ... She has been and always will be a great inspiration to me. My deepest condolences to her family and loved ones.