Prince Philip had Queen Elizabeth’s three-karat diamond ring made with diamonds from one of his mother’s (Princess Alice of Battenberg, later Princess Andrew of Greece and Denmark) tiaras.

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A quick trip to the Tower of London will prove to any visitor that the Queen of England has many opulent options when it comes to what jewelry she can wear. Despite the ruby brooches, golden tiaras, and emerald chokers in her royal jewel box, there’s only one piece that she wears constantly—her engagement ring.

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The three-carat diamond ring, which Queen Elizabeth wears alongside her Welsh gold wedding band, was given to her by Prince Philip and Town & Country unearthed the incredibly sweet history behind the ring’s design. When Prince Philip was getting ready to propose to Queen Elizabeth, he knew he would need a ring fit for a Queen, so he turned to his mother, Princess Alice of Battenberg (later known as Princess Andrew of Greece and Denmark) for advice. She gave him a diamond-and-aquamarine encrusted tiara that she had been given as a wedding gift.

As Town & Country notes, the history of the diamonds themselves is fascinating. Princess Alice, who was Queen Victoria's great-granddaughter, was given the diamond tiara by Tsar Nicholas II and Tsarina Alexandra of Russia, the last members of the Romanovs and the Russian royal family.

WATCH: 100 Years of Breathtaking Engagement Rings

Prince Philip took the diamonds from the tiara and, like many of us commoners who re-use heirloom jewels, re-purposed them into an engagement ring with the help of a local jeweler. The resulting ring is a brilliant-cut diamond solitaire with five pavé diamonds on each side all in a classic platinum setting.

Prince Philip gave Princess Elizabeth the ring in 1947 and the rest is history.