Prince Joachim and Princess Marie traveled to Denmark to attend their nephew Prince Christian’s 18th birthday gala dinner. The Prince and Princess, who now reside in the United States, were accompanied by their two children, Count Henrik and Countess Athena, as well as Count Felix, one of Joachim’s sons from his first marriage.

©Count Nikolai

It was announced in March that the royal couple would be moving to Washington, D.C. this past summer because Joachim was set to begin a new position at the Danish Embassy in September.

Missing from the Danish royal family celebration on Oct. 15 was Joachim’s firstborn, Count Nikolai of Monpezat. Queen Margrethe II’s eldest grandchild is currently spending a semester studying at the University of Technology in Sydney, Australia. While he wasn’t present for his younger cousin’s celebration in Copenhagen, Nikolai did mark Christian’s milestone birthday with an adorable throwback photo of the two of them seemingly arm wrestling while the royal family watched the Hubertus Hunt Race in 2010.

Nikolai, 24, posted the picture to his Instagram Story, writing: “Funny how time flies 😆 13 years ago.” “Happy 18th Christian! Hope everyone celebrates you just as you deserve,” he added with a disco ball and dancing emojis.

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Queen Margrethe hosted a gala dinner for Prince Christian on Sunday at Christiansborg Palace. Future monarchs Princess Ingrid Alexandra of Norway, Princess Catharina-Amalia of the Netherlands, Princess Elisabeth of Belgium and Princess Estelle of Sweden were among the guests at the celebration, where Her Majesty surprised everyone with a concert performed by Benjamin Hav & Familien.

The evening ended with Christian walking on stage and expressing his appreciation for those who attended. He said, according to the Royal House (translated to English), “It has been an absolutely unforgettable evening and I really appreciate that you all came from far and wide to celebrate me!”