Grease: Olivia Newton-John and John Travolta's roles of a lifetime

Grease may have just celebrated its 44th anniversary since it was released on August 3, 1978, but the movie lives on in the hearts of millions.

Olivia Newton-John was 29 years old and John Travolta 23 years old, when they teamed up to play one of history's most well-known movie couples.

Word is that Travolta had to convince Newton-John to be in the movie as she feared she was too old to play a high schooler.

The film, based on the musical set in the 1950s, captures the joys, sorrows and shenanigans of the couple during their final year of high school. Tell me about it, stud.

Despite some debate these days that the film may have arguably portrayed an endorsement of rape culture and slut-shaming; the 50s nostalgia, killer songs and unforgettable performances by Newton-John and Travolta have kept audiences coming back for decades.

After all, Sandy did change from "too pure to be Pink" into a smokin' bad girl in the final scene of the movie.

To mark its significant anniversaries since it was released, Grease has been re-released into cinemas, and for the lucky few who remember drive-in movies it was also re-released there.

These days the movie has fan groups and is regularly a stage show somewhere in the world.

And, as news broke of Newton-John's death on Tuesday, John Travolta acknowledged that Grease and the duo's roles as Danny and Sandy were among their most well known.

In an emotional post on Instagram, Travolta paid tribute to his former co-star.

"Your impact was incredible. I love you so much. We will see you down the road and we will all be together again. Yours from the first moment I saw you and forever! Your Danny, your John," he said.