I kind of think of them as that was then, they’re forever and so like that."

Travolta posted a photo of Newton-John toInstagramalong with a heartfelt caption.

“My dearest Olivia, you made all of our lives so much better.

John Travolta and Olivia Newton-John smiling

Your impact was incredible.

I love you so much.

We will see you down the road and we will all be together again.

Olivia Newton-John and John Travolta smiling together

Yours from the first moment I saw you and forever!”

He signed it as “your Danny, your John.”

Over the years, Newton-John and Travolta remained friends, and “Grease” has remained a fan favorite.

Olivia Newton-John and John Travolta smiling at Grease premiere

“We did something life-changing, making that film,” Newton-John toldPeoplein 2018.

“[At the premiere] you got the feeling from the energy that something was happening.

It was a huge response.

I feel grateful to be a part of that and to have worked with him.

We’ve stayed friends ever since.”

“[In tough times] John always reaches out to me,” she said.

I’ve been through her having a child, getting divorced, losing her sister.

She’s been through my getting married, having children.

It’s wonderful and full of shared memories."