The diamond jewel was borrowed from the Queen and could be worth more than £1million, according to gemologist and jewellery expert Deborah Papas.
She said: “It is very hard to estimate the value but as a Cartier piece, I would estimate it to be worth approximately £750,000 to £1.25million.”
Lover’s Knot tiara
Before Kate wore the headpiece, it had been worn by royals including Princess Diana.
The large tiara is covered with diamonds and pearls and could reportedly fetch as much as £18million.
It is thought to be made up of 85 carats of diamonds with 19 natural pearls.
The Lotus Flower tiara
Previously a favourite of Princess Margaret, Kate has worn the Art Deco piece on two occasions.
Speaking about the tiara Alexandra Michell, Gemologist Prestige Pawnbrokers Hatton Garden, said: “The Lotus Flower tiara was commissioned by the Queen Mother in 1923, converting a gift from her husband George VI. The gift in question was a diamond necklace from Garrard, which had a completely different Grecian design.
“A historical and stylish piece such as this, would no doubt achieve in the regions of £4million.”
At the end of 2019, Kate borrowed a pair of glitzy teardrop earrings that were first worn by Queen Elizabeth II in 2012.
While their value is not known, they are sure to be worth a small fortune due to their rarity and royal link.
Irish Guards Brooch
The brooch was worn by Princess Anne when she handed out shamrocks to celebrate St Patrick’s Day each year from 2002 to 2011.
Kate has continued to wear the gold pin since taking over the role from Princess Anne in 2012.