Martin A. S. Hume,
The Court of Philip IV.: Spain in Decadence
“ The Duke of Braganza, the Portuguese pretender with the best right to the throne, was prodigiously rich and over cautious, but his virile Spanish Guzman wife was eager and ambitious; whilst her wealthy brother, the Duke of Medina Sidonia, head of the Guzmans, silently helped forward the scheme which would make his sister a Queen, and afford him, the most powerful vassal of the Castilian crown, a precedent for the creation of an independent principality for himself in Andalucia, free from the weak and corrupt bureaucracy led by his cousin Olivares in Madrid. ”
