I don't know if you already found the answer to your query, but the necklace and earrings worn by the Duchess of Edinburgh are part of a Sapphire and Diamond demi-parure. There is a bracelet in the set too. They are quite lovely pieces and I hope we will get to see the Duchess wear the necklace more often. From what I have been able to find this is the first time the necklace has been worn publically. The earrings on the other hand have been worn previously. They were in fact worn for the Coronation of the King and also at an evening event in Gibraltar in 2022. The set is reportedly from the renowned jeweller Graff.