Olivia Newton-John has shared why she could never date John Travolta when filming Grease.

It appears to be the norm that co-stars who play each other’s love interests in films inevitably end up dating. The couples who have translated their on-screen relationships to off-screen romances are countless: Zac Efron and Vanessa Hudgens, Kristen Stewart and Rob Pattinson, Brad Pitt and Angelina Jolie. But never John Travolta and Olivia Newton-John.

Despite fans always wanting them to date, they insisted they always have, and always will be, friends; in fact, she has described her affection for him as “sisterly”.

Now, Olivia Newton-John is revealing why she and John Travolta never did date when they filmed the hit film Grease in 1978.

Talking to Mia Freedman on the No Filter podcast, the actress revealed why that it is, and why their connection on screen was better for it.

“We were both with other people when we were filming and I think, respectfully, it just didn’t happen,” Newton-John, who played Sandy, explained to Freedman.

“I think it was good, because I think it kept the tension there and the chemistry. It might have been a real disaster had we decided to date or we had a falling out or something. So I think it was just as well that it didn’t happen. But we’re still great friends.”

Olivia Newton John was 28 years old when she played the role of Sandy, and she reveals in her new book, Don't Stop Believin', that she initially passed on the role in Grease because she thought "Sandy was someone else's role."

However when John Travolta, who was already cast for the lead male role of Danny, went to visit her, he apparently told Olivia, "There was only one person on this planet I could see as Sandy, and that person was Olivia Newton John. I told the producers."

Olivia was convinced, and they filmed the movie in the summer of 1977.

As Freedman said, not all co-stars stay as close as Oliva, John and the rest of the cast have. To which Olivia responded, "Those times in your life that are really special, it's lovely to keep in contact."

"I have friends from childhood and, I have friends from all my life," she explained.

You can listen to the full No Filter podcast with Olivia Newton-John here...

You can purchase Olivia Newton John's new book, Don't Stop Believin', here.