At their wedding, Kate was given a wedding band made from Welsh gold, in line with royal tradition.
Since then, she has worked as a full-time member of the Royal Family which sometimes involves attending very important royal events.
On such occasions, the Duchess of Cambridge has sometimes borrowed pieces of royal jewellery.
However, she has recently been spotted wearing a piece that is not part of any royal collection.
The mother-of-three has attracted attention by wearing a ring that could be worth a huge amount of money, according to managing director at Miltons Diamonds Ben Johnson.
“The ring looks like a very large citrine stone to me and judging by the size of it could be worth anything from £5,000 up to £20,000,” he told Express.co.uk.
“Media reports have suggested that this ring is a new addition to the Duchess of Cambridge’s collection.
“But there is proof she owned it already, as she was photographed wearing it on a night out with Pippa in 2008.”
“This would explain the motivation behind Kate’s decision to wear it on occasions when she is not accompanied by the Duke of Cambridge, attending events on her own terms.
“She is an experienced royal now, capable and independent.”
Kate has been part of the Royal Family since 2011 and her choice of jewellery could confirm her growing confidence in her senior role.
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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 became the Duchess of Cambridge on the day.