Olivia Newton-John recently celebrated her 71st birthday. Her longtime friend of over 40 years, John Travolta, was quick to honor his friend for her birthday in an Instagram post. Travolta shared a photo of the two from the set of the hit musical movie Grease in 1978\u00a0and added a sweet caption to match. "Happy Birthday Olivia! All my love, JT," the caption says. If you swipe right on the Instagram collage, you can see a recent photo of them from the 40th-anniversary screening of Grease. John Travolta honors Olivia Newton-John with old 'Grease' photo John Travolta, Olivia Newton-John \/ Instagram The two actually met for the first time on the set of the film, where he played bad-boy Danny Zuko and she played good girl Sandy Olsson. Their characters meet from different parts of the world and soon enough they find themselves now attending the same school when Sandy's family ends up staying in America for good (as she as originally from Australia). The two end up falling in love and staying together despite being from two different worlds, literally and figuratively. Newton-John recently opened up about her transformation into "bad Sandy" at the end of the film and how much attention she got from being all dolled up like a bad girl! Newton-John remembers "Bad Sandy" Cast of Grease \/ Paramount Pictures \u201cLooking back, how was it transforming into a bad girl in\u00a0Grease?\u201d\u00a0Fox News\u00a0asks the star. In short, Newton-John says transforming into a bad girl at the end of the film was so much fun! \u201cI was playing Sandy for quite a while on set and I got to know her as this sweet little girl in a poodle skirt,\u201d she says. \u201cI walked on set wearing the costume while\u00a0John was in the middle of filming a song. The reaction I got was so unexpected *laughs*. First of all, didn\u2019t know who I was. And then I got all of this attention from the guys. I just thought, \u201cOh my goodness! Is this what it takes?\u201d *laughs*.\u201d An update on Newton-John's cancer battle: She's Doing Well! Olivia Newton-John \/ Denise Truscello As far as Newton-John\u2019s battle with cancer goes, it sounds like she\u2019s doing pretty well these days! She says that last year in September she was \u201cbedbound,\u201d but now she\u2019s doing \u201cgreat.\u201d When asked if she is in\u00a0remission\u00a0yet, she has a simple yet thought-provoking answer. \u201cI don\u2019t call it remission \u2014 I just say I\u2019m living with it. I\u2019m living with it very well. To think that you could get rid of every single cell is not really a reality at this point. But I\u2019m feeling great. Things are shrinking.\u201d Newton-John has been very open in regards to\u00a0her usage of medical cannabis during her cancer battle. It seems to have helped a ton! Olivia Newton-John and family \/ Instagram Didi Conn Talks About Olivia Newton-John\u2019s Cancer Battle: \u201cShe\u2019s Doing Beautifully Well\u201d.