Kate the great!

The Duchess of Cambridge was all smiles at a white tie affair at Buckingham Palace Tuesday evening, looking radiantly regal in one of her “favorite” tiaras – the Lover’s Knot – which was once similarly favored by her late mother-in-law, Princess Diana.

Duchess Kate looked every inch the royal in an embellished, off-white cap-sleeve gown by Jenny Packham and the historic headpiece for the annual Diplomatic Reception, ABC reported.

Duchess Cate greets guests at an evening reception for members of the Diplomatic Corps at Buckingham Palace on Dec. 4, 2018 in London. Approximately 7,500 military personnel are currently serving overseas at Christmas.  (Victoria Jones - WPA Pool/Getty Images)

As noted by Page Six, the sparkler is shaping up to be one of her favorites; the 36-year-old mother of three last wore it just weeks ago to a state banquet on Oct. 23.

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On loan from Queen Elizabeth, the Lover's Knot diamond-and-pearl tiara was made in 1914 for Queen Mary, according to Harper's Bazaar.

The late princess last wore the crown in 1991, and it remained unseen in the public eye until Kate stepped out in it in 2015.

Royal expert Victoria Murphy told ABC that a headpiece as sentimental as the Lover’s Knot is perfectly fitting for an occasion like the formal Diplomatic Reception.

“It’s a white tie event so its possibly the glitziest event in the royal calendar. You don't get any more dressed up than white tie events. [Kate wore] what is proving to be her favorite tiara actually — the Lover's Knot.”

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After enjoying what was surely a delightful evening, Kate and her husband, Prince William, were back to business on Wednesday morning, jetting to Cyprus to meet with Royal Air Force service members stationed there, ahead of the holidays.