Mr Hird added: “Kate Middleton’s engagement ring has possibly the most history and heritage out of all the royal engagement rings.

“Designed by Garrard & Co, the ring was originally part of a collection made for Diana to choose from, as requested by Prince Charles.

“At the time, the ring was valued around £28,000 to £47,000 and has since increased in value to an estimated £390,000 – already making it the most expensive of all the royal engagement rings.

“But due to the ring’s history, the ring is considered almost priceless.”