The couple's eldest child, Prince Christian, will mark his 18th birthday on 15 October with a gala dinner at Christiansborg Palace in Copenhagen.
Guests will include a selection of the country's youth organisations and rising stars, as well as members of foreign royal families.
Invitations have been sent out by the Danish royal palace, which dictate the lavish dress code.
In a snap shared by Gert's Royals on X, the platform formerly known as Twitter, the invitation hints at tiaras for any royal ladies in attendance.
"Galla B (B meaning Ballgown)/Uniforms/ White tie/ Gowns Decorations (Honors) and Tiaras may be worn."
Prince Christian's grandmother, Queen Margrethe, who will play host, and his mother, Crown Princess Mary, have plenty of jewels to choose from in the royal vaults.
However, Christian's sisters, Princess Isabella, 16, and Princess Josephine, 12, are unlikely to wear tiaras until they reach the age of 18.
Norway's Crown Prince Haakon and his daughter, Princess Ingrid Alexandra, 19, have already confirmed their attendance at the gala dinner, along with Sweden's Crown Princess Victoria, Prince Daniel and their 11-year-old daughter, Princess Estelle.
Other royals who could be in attendance at the dinner could include King Willem Alexander and Queen Maxima of The Netherlands, along with their two eldest daughters, Princess Catharina-Amalia, 19, and Princess Alexia, 18.
King Philippe, Queen Mathilde and Princess Elisabeth, 21, of Belgium may also be among the royal guests.
On the morning of his 18th birthday, Christian will appear on the balcony of Frederik VIII’s Palace together with his family and Queen Margrethe.
And in another milestone, as a future king, Christian will participate in a meeting of the Council of State, at which he will make a so-called solemn declaration that he will abide by the Constitution.
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