Willem’s grandfather Johannes Castelein was a Dutch petroleum engineer who was sent over to what was then the Dutch East Indies in 1930 to work for Shell. He was assigned to a port town in East Java. This had a large enough expat community to support a school to which most of the local Dutch and mixed-race population, as well as Chinese merchants, sent their children. He met, fell in love with, and married Greta, who was a teacher there. They had three children during the 1930s: Ruud, a boy born in 1932; Mina, a girl in 1934; and Hendrik, Willem’s father, in 1937.