Click on the photos below for a gallery of Kate's engagement ring.
"Everyone wants to copy Kate," said diamond expert Vashi Dominguez, founder of online jewellers Vashi.com. "We never had replicas of her ring because we thought it would never sell. But since she started bringing it out, it's just sold really well.
"We've had sporadic demand for rings inspired by celebrities like Kim Kardashian, Angelina Jolie, Jennifer Aniston, Beyoncé and Natalie Portman but this one inspired by Kate Middleton — everyone wants it. Every teenager, anyone in their twenties wants it."
The ring in question — a 12-carat oval Ceylon sapphire surrounded by a cluster of 14 diamonds set in white gold — was given to Kate by her husband Prince William in 2010, after the second-in-line to the throne proposed on a romantic holiday in Kenya.
Since the news was announced, Vashi has seen a whopping 300 per cent rise in the sales of his company's replica ring, which is about two and a half times smaller than Kate's and about eight times lighter.
Kate's ring reportedly cost £28,000 when Prince Charles bought it in 1981 to present to Princess Diana. While the "people's princess" debuted it shortly after the proposal, Vashi noted that the ring's popularity took off when Kate brought it out again.
"With Diana, everyone loved her but there was always a lot of controversy surrounding her marriage and death," said Vashi. "It's not so much that Kate is royalty so people feel they have to respect her. People genuinely really like her.
"Britain is a very traditional nation but I think Kate changed the way people think. They've always been very conservative and would have looked at something like this, and thought, 'This isn't an engagement ring. You've got to take it seriously – it isn't a fashion piece.' But now it's become the classic engagement ring."
A booming trend that Vashi's business has seen is to incorporate coloured gem stones into engagement rings, just like Kate's. The most popular colour asked for is blue, followed by red then pink. Vashi added that sales for rings with blue sapphires, one of Princess Diana's favourite gemstones, increased by 15 per cent in the UK since Kate's engagement.