John Travolta makes heartfelt Instagram tribute to 'Grease' co-star Olivia Newton-John on the late singer's birthday

John Travolta has paid tribute to Olivia Newton-John on what would have been her 74th birthday on Monday. Newton-John was born on Sept. 26, 1948. The singer, actor and philanthropist, died on August 8 after a long struggle with breast cancer.

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