Floral Aigrette Tiara and the set of rubies, diamonds, and pearls that belongs to the Danish crown jewels. Using the dress and jacket again for later official portraits, she used the Pearl Poire Tiara and the pearl and diamond jewels that are often worn with it (and I do prefer the pearl tiara with this, despite my deep love for her flexible floral diadem).
The whole effect is intended to be rather Holbein-like, and fittingly, she also wore this for a very imperious portrait by Thomas Kluge (you may know him from a slightly more infamous portrait of the royals). The whole look borders on overwhelming, but it's such a good match to its wearer, I can't help but love it. The Queen mentions in Dronningens Kjoler by Katia Johansen that this dress could someday replace the blue court dress with fur trim she's been using for the daytime New Year's Courts for so many years, and I, for one, can't wait for that day to arrive.
Photos: via Getty Images as indicated, DR video, Rigmor Mydskov/Kongehuset.dk