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"It was unforgettable," said a beaming King Willem-Alexander, who turns 47 on Sunday. "De Rijp and Amstelveen, heartfelt thanks to you from me and my family."
The royal couple were joined by their three daughter Princess Catherina-Amalia, Princess Alexia and Princess Ariane as they took part in the national day's activities, including in a river pageant on the river Amstel.
Relive King Willem-Alexander's inauguration
Other members of the Dutch royal family turned out for the celebrations in the cities of Amstelveen and De Rijp, including Princess Beatrix, Princess Laurentien and her husband Prince Constantijn.
Saturday festivities marked the country's first King's Day, Koningsdag in Dutch, given that it is the first time the annual celebration has fallen since Willem-Alexander's inauguration on 30 April 2013, before which it was Queen's Day.
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Across the country, in the streets, canals and parks, people enjoyed parades, live music, DJs, parties and street markets with flowers, flags and orange banners addorning the roads to add to the vibrant atmosphere.
King Willem-Alexander and his Argentinean wife Maxima took to the Dutch throne following Queen Beatrix's abdication last year.
Thirty-three years after she took the throne Beatrix gave up her role as head of the House of Orange in a solemn abdication ceremony and has since reverted to her original status as a princess.
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Royals from around the world, including Prince Charles and the Duchess of Cornwall, Prince Frederik and Princess Mary of Denmark and Princess Victoria and Prince Daniel of Sweden, flocked to Amsterdam to see Willem-Alexander sworn in, making his 10-year-old daughter Princess Catharina Amalia first-in-line to the throne.
According to HELLO!'s sister publication HOLA! 87 percent of the Dutch population believe that their new monarch has done a "good or very good" job in his first year, although some analysts have said it is too early to tell given that King Willem-Alexander has not been faced with many significant challenges in his first 12 months.