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AMSTERDAM, THE NETHERLANDS - NOVEMBER 28: King Philippe and Queen Mathilde of Belgium and King Willem-Alexander and Queen Maxima of The Netherlands attend the signing of the treaty Boundary Correction by Belgian and Dutch foreign Ministers Reynders and Koenders at the Royal Palace on November 28, 2016 in Amsterdam, Netherlands. (Photo by Patrick van Katwijk/Getty Images)

AMSTERDAM, THE NETHERLANDS - NOVEMBER 28: King Philippe and Queen Mathilde of Belgium and King Willem-Alexander and Queen Maxima of The Netherlands attend the signing of the treaty Boundary Correction by Belgian and Dutch foreign Ministers Reynders and Koenders at the Royal Palace on November 28, 2016 in Amsterdam, Netherlands. (Photo by Patrick van Katwijk/Getty Images)