John Travolta is mourning the loss of his close friend and Grease co-star Olivia Newton-John, following her death aged 73.MORE: Olivia Newton-John opens up about health amid cancer battleThe actor shared a heartbreaking tribute to Olivia on social media shortly after her death was announced on Monday.On Tuesday, Richard Wilkins, Australia's Nine entertainment editor, appeared on Good Morning Britain, revealing that he had spoken to John via text message.VIDEO: Grease star Dame Olivia Newton-John dies aged 73He said that the actor was "too raw to talk" and understandably devastated by the news.MORE: Ella Travolta shows support for John Travolta following Olivia Newton-John's deathMORE: John Travolta's daughter Ella receives sweet message from Olivia Newton-JohnHe also said that Olivia was a "beautiful, warm, loving person," and that she "just radiated goodness."He added: "She was there for everybody all the time. She was so generous...