The royal couple, who were presumably in the early stages of their relationship when the footage was filmed, was seen holding a clear glass bottle.
Diana is shown how to do it by a member of the group, while Prince Charles turns around to face away from her.
With a cheeky grin on her face, Diana then slams the bottle over his head.
The sugar glass shatters everywhere and the room explodes with laughter and cheers.
Charles saw the humour too, laughing as he shook off the remnants from his hair.
Commenters on the video flocked to share their enjoyment of the resurfaced clip.
'She's so cute,' one wrote, with others just adding laughing emojis.
In a recent biography of Prince Charles, claims were made as to why he and is current wife Camilla Parker-Bowles didn't marry originally.
Almost a decade before his wedding to Diana, in the English Summer of 1972, Charles and Camilla began what would be the start their highly strung out relationship.
Camilla's long-time on-again-off-again boyfriend Andrew Parker-Bowles was out of the country on army service, and while he was away the duchess began a romantic relationship with Charles.
Sally Bedell Smith, author of Prince Charles: The Passions And Paradoxes of an Improbable Life, has made new claims that Camilla's meddling father is to blame.
In January 1973, Charles and Camilla were forced to seperate after he set sail for the Caribbean for naval duty. It was at that point that Andrew Parker-Bowles made his way back to London.
Bedell Smith makes claims that it was in fact, Camilla's family that wanted her to marry Andrew rather than the heir to the British throne.
'They intervened by publishing an engagement notice in The Times on March 15. His hand publicly forced Andrew proposed to his girlfriend of nearly seven years,' Bedell Smith writes.
By publishing an untruthful engagement notice, Camilla's father changed the course of history.
When Charles was back in port a few days later, he heard the news of Camilla's engagement and was understandably shocked.
According to Bedell Smith, Charles 'couldn't understand how "such a blissful, peaceful, and mutually happy relationship" had ended so abruptly, after such a promising start.'
If Andrew hadn't been forced to propose, Charles may have married Camilla first — instead of carrying on a disastrous affair with her during his marriage to Diana.
Bedell Smith further claims the couple didn't marry due to the royal family perceiving Camilla as an 'experienced' woman. Smith claims the duchess wasn't seen by the royal family as 'aristocratic' enough for the next in line for the throne.
Prince Charles' great uncle, Lord Mountbatten, reportedly advised the prince, 'Lovely for you two to have a fling, but this absolutely cannot end in marriage,' Express claims.
This article originally appeared on New Idea.