The hidden detail sewn in Queen Elizabeth's coronation gown

While King Charles III's exact coronation outfit remains a mystery, it's likely to include some decadent robes and items that will go on to be referenced across history.

Just like it has been for the late Queen Elizabeth's Sir Norman Hartnell coronation gown back in 1953, which has gone on display a number of times over the years - most recently to commemorate her Platinum Jubilee last June.

The famous gown had a secret element even Her Majesty didn't know about at the time.

READ MORE: How King Charles' coronation will differ to that of his mother

"They went through nine different designs, so the Queen thought that she really knew everything about this incredible piece of clothing," Bethan Holt, author of The Queen: 70 years of Majestic Style, tells 9Honey.

"But actually, Norman Hartnell embroidered a four-leaf clover inside the gown as a kind of emblem of good luck on this monumental day for such a young woman.

READ MORE: Meet the man organising the King's coronation

"You know, it was a huge moment, the Coronation, she must have been very nervous. So she probably needed all the luck she could get."

It remains to be seen if King Charles follows suit with a special good luck charm worked into his outfit.

The gown was commissioned eight months before the Queen walked into Westminster Abbey on June 2, 1953.

It took a team of six embroideresses approximately 3000 hours over nine weeks to complete the white duchesse satin gown, which was similar to the monarch's wedding dress.

The intricate design featured floral emblems in gold and silver thread and pastel-coloured silks, encrusted with seed pearls, sequins and crystals.

These represented nations across the UK and Commonwealth that the Queen was now sovereign of, including a wattle to represent Australia.

It's something Meghan Markle later took inspiration from for her 2018 wedding gown, designed by Clare Waight Keller for Givenchy.

In Secrets of the Royal Palace, a documentary series which aired on UK's Channel 5 last year, art historian Jacky Klein revealed how the designer hid the good luck charm in plain sight.

"Unknown to the Queen, Hartnell added a secret detail which was a little four-leaf shamrock which he placed on her left skirt just underneath where her hand would be resting during the ceremony," she said.

Hartnell was among the guests in the Abbey on the day of the Coronation and recalled the dress having a "shimmering and sparkling" effect, Holt writes.

"Her Majesty told me graciously that the dress was triumphant," Holt quotes the designer.

It's not known when or how the monarch found out about the surprise good luck charm on her dress but it is thought to have been after the big day.

The gown will go on display at Windsor Castle as part of their Platinum Jubilee exhibit at Her Majesty's home, running from July 7 to September 26, 2022.

The Queen: 70 years of Majestic Style by Bethan Holt is out now.

Watch 9News' special coverage of King Charles' coronation for free on 9Now.