Stars are mourning the loss of beloved actress and singer Olivia Newton-John. The "I Honestly Love You" songstress died on Monday at her California ranch surrounded by family and friends, her husband announced in a statement. One of the first celebrities to pay tribute to her was her "Grease" co-star and longtime friend John Travolta. He wrote in part on Instagram, "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."