Olivia Newton-John and John Travolta will reunite to mark the 40th anniversary of their hit musical film 'Grease'.

The 68-year-old actress - who starred as Sandy in the 1978 iconic film opposite Travolta's Danny - has revealed they are still coming up with ideas of how they will celebrate the milestone, but they definitely have something in the works for 2018.

She told the Daily Mirror newspaper: ''We are thinking up ways. [We have] nothing to announce yet. 40 year anniversary of 'Grease', which I can't believe ... time goes so fast. It's so exciting.''

While there are no solid plans of what fans can expect, It's not the first time Olivia has shared their plans for a reunion.

In January, the Hollywood legend - who competed on 2015's 'Dancing with the Stars' - said she would love to get the cast together back together.

At the time, she said: ''I can't believe it's that long. I would like to do something special to help the hospital I work with, but I don't know if we could get the rest of the cast together.''

Olivia previously spoke of her fond memories of making the original movie in 1978, and how much ''fun'' she and her co-stars had.

She previously said: ''It was like going back to a school that I never went to.

''We were all in our late 20s and 30s, but we felt like we were teenagers, so I think the whole thing was a lot of fun from beginning to end. We had a great energy.''

Meanwhile, she has been vocal about her dislike of the 1982 'Grease' sequel, which starred Michelle Pfeiffer, which she and John turned down.

Olivia has no regrets about passing on the project.

Asked what she thought of 'Grease 2', she previously admitted: ''Not a lot.

''They did ask us, I think they approached John and I to do it, and then it didn't happen, and I didn't think it was gonna happen, and then they made it with other people.''

However, when it came to the TV special 'Grease Live!' -

which saw Julianne Hough in her role of Sandy and Aaron Tveit as Danny - Olivia had more positive things to say.

She said: ''I liked it. Yeah, it was fun.''