Aldaz’ maternal ancestors were distinguished Carlists; his great-great-grandfather José Miguel Arrieta-Mascarua served in 1843–1871 in the Cortes, while another one Andrés Bruno Quadra-Salcedo acted as high legitimist Biscay official during the Third Carlist War. His great-grandfather Tomás Pedro de la Quadra-Salcedo was a fuerista, while his grandfather Estanislao de la Quadra-Salcedo along 4 brothers volunteered to requeté; 4 of the siblings were either killed in action or executed by the Republicans. His mother was an ardent Carlist, active in the female organization Margaritas. Aldaz later claimed that growing up a Traditionalist was a natural way of maturing for him, that since childhood he participated in annual rallies at Montejurra, Montserrat or Isuskiza, and that as a boy he knew many Carlist Navarrese personalities. One of them, Amadeo Marco Ilincheta, was his godfather. It is not clear what was the role of the early Republican record of his father; as a mariner he later befriended Carlist mariners, in particular Marco Ilincheta and "Capitán Etayo".