Princess of Portugal (1535-1573) by marriage to John Manuel, Prince of Portugal. She served as regent of Spain to her brother Philip II of Spain during his trip to England to marry Mary I in 1554-1556, and from 1556-1559; in that role, she repeatedly intervened in favor of the new order of the Jesuits, founded by Ignatius of Loyola, with whom she corresponded. Rare manuscript DS in Spanish, signed “J. la Princesa,” four pages on two adjoining sheets, 8.5 x 12, June 28, 1559. Untranslated document signed at the conclusion by Joanna of Austria, Princess of Portugal, as regent of Spain. In very good condition, with scattered staining, and partial separation to the central horizontal fold.