Queen Margrethe will head up the white-tie dinner for her grandson at Christiansborg Palace in Copenhagen.
Earlier in the day, the royals will appear on the balcony of Frederik VIII’s Palace to view the Changing of the Guard.
A number of guests have already confirmed their attendance at Prince Christian's celebrations, including members of foreign royal families.
Christian's immediate members of his family will be in attendance – his parents, Crown Prince Frederik and Crown Princess Mary, as well as younger siblings, Princess Isabella, 16, and 12-year-old twins, Prince Vincent and Princess Josephine.
Queen Margrethe's younger son, Prince Joachim, and his wife, Princess Marie, are expected to fly over to Denmark from Washington D.C. in the US for the occasion, along with their children, Count Henrik and Countess Athena. Joachim also has two sons from his previous marriage – Count Nikolai and Count Felix.
Meanwhile, Crown Princess Victoria and Prince Daniel of Sweden will be among the foreign royal guests, and will be joined by their 11-year-old daughter, Princess Estelle.
Representing Norway will be Crown Prince Haakon and his 19-year-old daughter, Princess Ingrid Alexandra.
Future Belgian queen Princess Elisabeth, 21, has also confirmed her attendance.
Guests will also include a selection of the country's youth organisations, as well as youngsters who have made their mark in the worlds of sport, arts and culture.
The Danish court added: "In addition, The Royal House of Denmark will invite up to 200 young people from the realm to take part in the celebration in cooperation with the country’s municipalities, as each of Denmark’s municipalities as well as Greenland and the Faroe Islands will have the opportunity to select two 18-year-olds to participate in the gala dinner."
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Given the Danish royal family's closeness with other European royal households, other potential guests could include King Willem-Alexander and Queen Maxima, and their eldest daughters, Princess Catharina Amalia, 19, and Princess Alexia, 18.
Hereditary Grand Duke Guillaume and Hereditary Grand Duchess Stephanie of Luxembourg could also join the celebrations.
And it's yet to be seen whether Princess Maria Chiara of Bourbon-Two Sicilies will be at the gala dinner.
Chiara, who is the daughter of Prince Carlo, Duke of Castro and Princess Camilla, Duchess of Castro, dismissed rumours that she is dating Prince Christian in a statement shared on Instagram last month, writing: "Prince Christian and I share a close friendship."
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