According to Carl Duane's book 'With All Arms' and several other historical and genealogical references, Alonso de Estrada was the illegitimate son of Fernando El Catolico. Manuel Morales Munoz's book 'Los Altamiranos' states that Alonso, "who was the natural son of Ferdando El Catolico, Rey de Aragon, by the account of several historians and so recorded in the Holy Inquisition (of which I plan to research this summer 2004 in Madrid) Historical Archives of the Nation in Madrid Testimony 1501, No. 17...."