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TOPSHOT - King Willem Alexander, Queen Maxima and their daughters Amalia (2-R), Ariane (C) and Alexia (L) wave to the crowd as the king celebrates his 50th birthday in Tilburg on April 27, 2017. - The king's 50th birthday happens to fall on King's Day or Koningsdag formally known as Queen' Day until King Willem-Alexander ascended to the throne in 2013 following the reign of his mother. (Photo by Remko de Waal / ANP / AFP) / Netherlands OUT (Photo credit should read REMKO DE WAAL/AFP/Getty Images)

TOPSHOT - King Willem Alexander, Queen Maxima and their daughters Amalia (2-R), Ariane (C) and Alexia (L) wave to the crowd as the king celebrates his 50th birthday in Tilburg on April 27, 2017. - The king's 50th birthday happens to fall on King's Day or Koningsdag formally known as Queen' Day until King Willem-Alexander ascended to the throne in 2013 following the reign of his mother. (Photo by Remko de Waal / ANP / AFP) / Netherlands OUT (Photo credit should read REMKO DE WAAL/AFP/Getty Images)
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AFP REMKO DE WAAL

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Dutch Queen Maxima holds a ball during King's Day or Koningsdag celebrations in Tilburg on April 27, 2017. Dutch King Willem Alexander is celebrating his 50th birthday which happens to fall on King's Day or Koningsdag formally known as Queen' Day until King Willem-Alexander ascended to the throne in 2013 taking the reign from his mother. / AFP PHOTO / ANP / Koen van Weel / Netherlands OUT (Photo credit should read KOEN VAN WEEL/AFP/Getty Images)

Dutch Queen Maxima holds a ball during King's Day or Koningsdag celebrations in Tilburg on April 27, 2017. Dutch King Willem Alexander is celebrating his 50th birthday which happens to fall on King's Day or Koningsdag formally known as Queen' Day until King Willem-Alexander ascended to the throne in 2013 taking the reign from his mother. / AFP PHOTO / ANP / Koen van Weel / Netherlands OUT (Photo credit should read KOEN VAN WEEL/AFP/Getty Images)
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AFP KOEN VAN WEEL

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TILBURG, NETHERLANDS - APRIL 27: Queen Maxima attends the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)

TILBURG, NETHERLANDS - APRIL 27: Queen Maxima attends the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)
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French Select Patrick van Katwijk

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TILBURG, NETHERLANDS - APRIL 27: Queen Maxima and Princess Alexia attend the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)

TILBURG, NETHERLANDS - APRIL 27: Queen Maxima and Princess Alexia attend the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)
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French Select Patrick van Katwijk

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TILBURG, NETHERLANDS - APRIL 27: King Willem-Alexander, Princess Amalia and Princess Ariane attend the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)

TILBURG, NETHERLANDS - APRIL 27: King Willem-Alexander, Princess Amalia and Princess Ariane attend the King's 50th birthday during the Kingsday celebrations on April 27, 2017 in Tilburg, Netherlands. (Photo by Patrick van Katwijk/Getty Images)
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French Select Patrick van Katwijk