The last royal occupant of Het Loo was Queen Wilhelmina, having given to castle to the State in 1962. Now, her daughter, Queen Juliana, took up residence at Soestdijk Palace, which I can't find on the map. It would make a good addition to Virtual Globetrotting...
http://www.castlesontheweb.com/members/dutchcastles/hollandcastles/html/hetoudeloo.htm
http://en.wikipedia.org/wiki/Soestdijk_Palace