Though Queen Elizabeth's extensive collection of royal jewelry is arguably priceless, the monarch’s employees use quite a low-key liquid to keep gems sparkling -- gin.

Angela Kelly, the queen’s longtime dressmaker and personal assistant, shared the surprising secret in her new book “The Other Side of the Coin: The Queen, the Dresser and the Wardrobe,” published two weeks ago.

“A little gin and water come in handy to give the diamonds extra sparkle -- just don’t tell the jeweler!” the author teased, according to People magazine.

Queen Elizabeth's royal jewels are cleaned with a bit of gin to keep them extra sparkly.

Queen Elizabeth's royal jewels are cleaned with a bit of gin to keep them extra sparkly. (Getty)

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Citing another go-to jewelry cleaning trick, Kelly said that “a drop of washing-up liquid and water will get rid of any hairspray stains” when polishing diamonds and tiaras before formal occasions such as the State Opening of Parliament.

All DIY hacks aside, the queen’s most valuable baubles are, of course, inspected and sterilized by specialists, Kelly said.

“The queen’s jeweler will give the stones a deep clean when necessary, so for me, it’s just a matter of a quick polish and they’re sparkling once more,” she explained.

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President Donald Trump and Queen Elizabeth II toasted during the State Banquet at Buckingham Palace in June 2019.

President Donald Trump and Queen Elizabeth II toasted during the State Banquet at Buckingham Palace in June 2019. (AP)

Though the cleaning methods may seem a bit unorthodox, Kelly’s book was written with the “approval” of the nonagenarian ruler, according to People -- a regal stamp of approval if ever there ever was one.

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The stylist, who has worked for the royal family since 1994, is formally known as personal advisor and curator specializing in the queen’s jewelry, insignias and wardrobe, as well as in-house designer.