Kate Middleton chose to inspire her ensemble with a very high-end gift from Prince William.

Prince William or his wife spent Christmas Eve with their family at Sandringham.
https://www.instagram.com/princeandprincessofwales/?hl=en
He also joined his children Prince George, Charlotte or Louis at the event in Sandringham on Christmas Eve.
The gift given by the prince was discovered by The Sun who told everyone about the gift.
As you can tell, the princess upped the ante with this high-end gift: she was gifted a hundred ponds gold earrings by a very famous Parisian brand.
The gold earrings sold out online within seconds as royal fans couldn’t stop admiring them when the princess stepped out wearing them and rushed to admire them.
A girl said on the Twitter account that these are very lovely earrings or the princess is bound to love them. I want my husband was like William, who thought like her.