The sentimental diamond and platinum piece had been previously worn by the Queen mother, Princess Margaret and the Princess Royal.
Speaking to Express.co.uk, Deborah Papas, gemologist prestige pawnbrokers of Channel 4’s, Posh Pawn, revealed the history.
She said: “It has 149 baguette-cut diamonds as well as an astounding 739 brilliant cut diamonds of varying weights, with the largest being at the top in the centre.
“Most of the diamonds are small in comparison to the piece worn by The Duchess of Sussex but are subtle and beautifully set.”
Although the design is likely to stay in the Royal Family, it would be worth a staggering amount of money if ever sold.
“It is very hard to estimate the value but as a Cartier piece, I would estimate it to be worth approximately £750,000 to £1,250,000,” Deborah added.
Kate completed her wedding jewellery look with a pair of drop diamond earrings.
Meghan Markle also opted for a headpiece and walked down the aisle wearing the Queen Mary Diamond Bandeau tiara.
So, which tiara cost more?
Although the exact values of the tiaras are unknown, Deborah revealed Meghan probably snatched the pricier piece.
She explained: “It is hard to put a value on this little seen piece but could be worth up to £2million.”
How did Kate Middleton become a royal?
Kate Middleton, or Catherine, Duchess of Cambridge, was born on 9 January 1982 at the Royal Berkshire Hospital, Reading, England.
She was born to Michael and Carole Middleton, a former flight dispatcher and air hostess. The couple founded a party supplies company, Party Pieces, in 1987 – now estimated to be worth £30 million.
Kate has a younger sister Pippa Matthews, 34, and a younger brother James Middleton, 31.
Kate and her family moved to Amman, Jordan, in 1984, where the future Duchess was educated at an English-speaking nursery school.
After moving back to Berkshire the family sent Kate to private school, St Andrews School. She went on to briefly study at Downe House before moving onto Marlborough College where she boarded.
For university the young Kate attended the University of St Andrews in Fife, Scotland. Here she was awarded an undergraduate MA (2:1 Hons) in history of art.
Relationship with Prince William
Kate met Prince William when they were both studying at St Andrews, and both living in St Salvator’s Hall. Famously, William reportedly took a fancy to Kate after she wore a see-through dress during a fashion show.
In 2003 the couple began dating and lived together during their second year of university.
The couple split in April 2007, however, in October they were back together.
Prince William proposed to Kate Middleton with his late mother Princess Diana’s engagement ring in October 2010. The couple were holidaying in Kenya at the time.
On 29 April 2011 they married at Westminster Abbey with a whopping 26 million watching the event live.
Kate wore an Alexander McQueen dress worth a reported £250,000 on the big day.
Kate assumed the title “Her Royal Highness The Duchess of Cambridge” and also become the Duchess of Cambridge on the day.