It is very likely that Guill based his allegations on the claim made by Gaspar Frutuoso that Willem was the grandson of a Count of Flanders. However, the noble origin of Van der Haegen has been disputed by various posterior authors. The first of which, Diogos das Chagas, claimed in his manuscript "'Espelho Cristalino'" from 1646 that there were two people named Silveira: ""João de Silveyra, a very important man and great merchant (or cunning merchant)"", to whom Joost de Hurtere ("Joz de Utra") made many promises if he would agree to settle on the Azores, and another ""Guilherme de Silveyra of the Silveyras of Brandath"" who traveled to Flores and then São Jorge. In regards to the latter, das Chagas writes that the name Brandath is a linguistical corruption of Vandraga.