While Kate Middleton’s sister, Pippa, is busy planning her wedding to financier James Matthews (in which Kate will likely not be a bridesmaid, but Princess Charlotte WILL be a flower girl), Kate has had a few very exciting things of her own going on.

LONDON, UNITED KINGDOM - NOVEMBER 22: Catherine, Duchess of Cambridge attends a children's tea party with pupils from Oakington Manor Primary School in Wembley, at the Natural History Museum to celebrate Dippy the Diplodocus's time in Hintze Hall on November 22, 2016 in London, United Kingdom. (Photo by Yui Mok - WPA Pool/Getty Images)

Not only has she taken up with adult coloring books (which we TOTALLY approve of), but she’s been keeping up with her duties as the Duchess of Cambridge, attending the Diplomatic reception at Buckingham Palace Thursday.

LONDON, UNITED KINGDOM - DECEMBER 8: (L-R) Camilla, Duchess of Cornwall, Prince Charles, Prince of Wales, Queen Elizabeth II, Prince Philip, Duke of Edinburgh, Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge arrive for the annual evening reception for members of the Diplomatic Corps at Buckingham Palace on December 8, 2016 in London, England. (Photo by Dominic Lipinski-WPA Pool/Getty Images)

But it wasn’t what she did, but what she wore, that has the world abuzz. In addition to a stunning, floor-length red Jenny Packham gown, drop earrings and some noticeable wrist bling, Kate added a very special accessory atop her royal head.

Pulling out a royal crown for only the fifth time since becoming a member of the family back in 2011, Kate donned Princess Diana’s Cambridge Lover’s Knot tiara: a diamond-and-pearl piece that the Queen herself gave to Princess Di in 1981 as a wedding gift.

Wow. We can’t even begin to imagine how much wearing her would-be mother-in-law’s tiara must have meant to her. We CAN comment on how absolutely stunning she looks in the piece, however: Girl definitely did Prince Will’s mum proud.

Fingers crossed this won’t be the last we see of Kate in such gorgeous headwear!

Are you excited to see Kate wear the royal crown? Share with us @BritandCo!

(h/t ET, photos via Dominic-Lipinski + Yul Mok/WPA Pool/Getty)