On Tuesday evening, the duchess joined her husband, Prince William, in welcoming the Dutch royals for a lavish state banquet at Buckingham Palace.
Kate wore a stunning light blue Alexander McQueen gown to the function, coupled with a stylish up-do.
Known for her use of colourful gemstones and intricate settings, Kate wears a pair of earrings by the British labels to nearly every public engagement, both formal and casual.
It was a copy of one owned by her grandmother, Princess Augusta of Hesse, who married the first Duke of Cambridge, seventh son of King George III, in 1818.
Some speculated that a tiara is too precious to be flown overseas with Meghan for her to wear, but this seems unlikely, the reason the Duchess of Sussex didn't wear a tiara is more likely to do with the dress code for the event and what the other guests would be wearing for the occasion.
"Normally I'm a fan of what Kate wears, but this is truly very bad. 'What was she thinking".
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She regularly loans pieces out to younger members of the Royal Family.
The last time Kate's dresses caused such controversy was she stepped out in "frumpy" floral dresses by Erdem two nights running during the royal tour of Sweden in January 2018.
Nearly more striking than the tiara was Kate's huge diamond and peal necklace, which turns out to have been in the royal family for over 100 years.
The dress - made in a thick vintage-inspired fabric - featured a ruched bodycon fit on the torso and flared out in a fishtail style. The necklace, which also features pearls and diamonds was a gift to Queen Alexandra from King Frederick if Denmark was passed down to the Queen's Mother and has been in the monarch's extensive jewelry collection.