Kate Middleton fans freak out over her latest choice of tiara (PHOTOS)

The Duchess of Cambridge donned a tiara that was new for her tonight, but longtime royal watchers will recognize the piece’s very special significance.

The Duchess of Cambridge was spotted being driven to a private diplomatic reception at Buckingham Palace alongside her husband Prince William, Duke of Cambridge, wearing something gorgeous and sparkly atop her head — and it appears to be one of the late Princess Diana’s favorite tiaras.

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Kate appears to be wearing the Cambridge Lover’s Knot tiara, which was “given” — actually loaned for the length of her marriage from Queen Elizabeth — to Princess Diana as a wedding gift when she wed Prince Charles in 1981. It quickly became one of Diana’s signature pieces and she wore it to countless events and formal photoshoots until she and Prince Charles divorced.

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The tiara has not been worn since then, so royal watchers are obviously freaking out over its latest appearance.

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The tiara was created for Queen Mary in 1913 by royal jeweler Garrard, and upon her death in 1953 was left to Queen Elizabeth. It is a copy of one given to Augusta Hesse-Kassel, the first Duchess of Cambridge, as a wedding gift in 1818.

This is only the third tiara Kate has worn since her 2011 wedding to Prince William, and the fourth formal occasion where she has worn one. She wore the Halo tiara to her wedding and the Lotus Flower tiara to the same diplomatic reception last year, as well as to Britain’s official state dinner for China President Xi Jinping in October 2015.

These few glimpses of Kate in the car on the way to the reception are likely the only ones we will see, as the event is private and no official photos are released to the public.

Princess Diana Kate Middleton slideshow