The couple got engaged in November 2010 after they first met at the University of St Andrews.
The mother-of-three was given the sapphire and diamond engagement ring that Prince Charles previously gave to Princess Diana.
Kate will usually wear the jewel when she steps out and it could have a huge price tag, experts at Joshua James Jewellery told Express.co.uk.
They said: “Kate’s engagement ring is incredibly famous, known for sparking a huge increase in sales of sapphire engagement rings back in 2010.
“It features a 12-carat oval sapphire set in 18k white gold, surrounded by 14 solitaire diamonds.
“Created by Garrard & Co. (the former Crown Jeweller), it is now valued at around £300,000. However, much of its value is sentimental: this engagement ring was passed down from Princess Diana, William’s mother.”
Not only is the ring worth a fortune, it is sure to mean a lot to Kate and William due to its link to his mother.
Members of the Royal Family are usually given a wedding ring made from Welsh gold.
Kate will wear her gold band on her wedding finger and it could be worth a whopping £2,000.
The experts continued: “Kate’s simple gold wedding ring is crafted from a special nugget of Welsh gold (a tradition that dates back to 1923) by Wartski, a jewellers based in London.
“The value of a Welsh gold ring depends on the weight and purity of the gold used, but will likely be upwards of £2,000.
“The plain, slender band shows off the incredibly rare and beautiful gold that it was made from, free of decorative elements that embellish many modern wedding rings.”
While it is common to wear an engagement ring and wedding band after getting married, Kate attracted attention with a third ring.
Shortly after the birth of their eldest son, Prince George, seven, in 2013, the royal was spotted wearing another small band on her wedding finger.
Many believe the white gold jewel was a gift from Prince William to celebrate the birth of their son.
The jewellery experts continued: “The third ring she wears is an eternity ring. Eternity rings are often used to mark special milestones in a relationship.
“In this case, it was a gift from her husband to mark the birth of their first child, Prince George.
Made from 18ct white gold, it features 0.23ct of white diamonds.
“Kate’s eternity band comes from London-based designer Annoushka, and is valued at £1,200.
“Many women choose to wear all three rings (wedding, engagement and eternity) on their wedding finger following marriage.”