This bracelet belongs to the Queen. It was one of two pieces commissioned by the Duke of Edinburgh as wedding gifts for his bride in 1947. Made of platinum, it is encrusted with diamonds taken from a tiara that had belonged to Philip's mother, Princess Andrew of Greece & Denmark, who had been given the tiara by Czar Nicholas II and his wife Alexandra. The cuff-bracelet has been worn often by Her Majesty the Queen.
Historical source: From Her Majesty's Jewel Vault blog.