Kate and Prince William married on April 29, 2011 and the wedding took place at Westminster.
The Duchess of Cambridge added to her ring collection on the big day as she was given a wedding band made from Welsh gold.
Kate has worn it next to her engagement ring since the couple married.
A few years after their ceremony, some royal fans may have noticed she started to wear a third ring on her finger.
The white gold band is believed to be an eternity ring given to the royal by Prince William to celebrate the birth of Prince George, seven.
Speaking to Express.co.uk, 77 Diamonds managing director Tobias Kormind suggested there could be a sweet meaning behind the jewel.
He said: “The gift of an eternity ring is an enormously romantic gesture that every woman dreams of.
“It represents undying, everlasting love – this is why it usually features identically-cut diamonds set all around the band to symbolise an eternal bond.
“A thread and grain setting is where the gold metal border is visible around the diamonds and there are small precious metal claws holding each individual diamond.
“I estimate a ring like this would be priced at around £1,500 to £2,000 on the high street.”
Since Prince George was born in 2013, Kate has worn the jewel on countless occasions.
The mother-of-three will often wear it on her wedding finger as is tradition for eternity bands.
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The royal line of succession – who outranks who?
The line of succession to the British throne dictates the order in which each member of the Royal Family would ascend to the throne.
It is also seen as a ranking of importance with the head of the line, the Queen, taking the place of ruler.
Older children come before younger children. Traditionally boys came before girls, but this law was changed on 26 March 2015 before the birth of Prince William’s first child.
Incredibly, Catholics are still excluded from the line of succession, as are children born outside of wedlock.
The royals, who usually stick to a strict protocol when appearing in public, often arrive at events in ascending order of importance, with the most important royal arriving last.
Prince Charles, 72, is currently first-in-line to the British throne, followed by Prince William, 38, his oldest son.
Then comes Prince William’s children, George, seven, Charlotte, five, and Louis, two, and they are followed by Prince Harry, 36. Prince Harry is succeeded by his son Archie Harrison, born in May 2019.