They're doing a territory exchange for the second time in 175 years or something like that, and Dam Square where they do this kind of stuff is in the middle of my commute so got to see the pomp and circumstance. Here is a pic of Dutch King Willem-Alexander and Queen Maxima waiting for the Belgians, and here is a video of the two kings inspecting the troops (the Belgian is the silver-haired fellow, the Dutch the red).
Interestingly, I saw the Spanish king a few months ago randomly in Spain leaving a party, so a monarch trifecta is in play.