I am almost finished a wonderful book, Sister Queens, by Julia Fox, concerning two of the daughters of Ferdinand and Isabella (of Aragon and Castile, respectively). Queen Katherine, of course, was the first wife of Henry VIII, and Queen Juana was the wife of Philip, son of Maximilian, Holy Roman Emperor (later dubbed "Juana the Mad"). We are quite familiar with the story of Henry -- who put away Katherine out of dynastic concerns, but this is the first account I've found that follows her life entirely -- from childhood, through putative marriage to Arthur, widow, negotiator, remarriage, and as a loyal daughter of Spain.
Also, it gives a compelling account of Juana -- explaining how she was manipulated by the men around her (husband and father) to be accounted mad for their own ends. I will give a full review of it when finished, but in the waning days of summer, you may want to pick it up and see history from an entirely different angle.