In the biography of Sir Edward Hyde, his visit to Madrid between November 1649 and March 1651 has usually been neglected for the little that is known about it is largely found in the episodes recalled nearly two decades later in Book XIII of his History of the Rebellion. Yet his sojourn, for close to a year and a half, at the court of Philip IV deserves attention since during it he published anonymously in Spanish an eloquent short pamphlet defending the legitimacy of Charles II’s right to the English throne, while he denounced the Commonwealth as a tyrannical usurpation of authority without a basis in English law or the law of nations. The occasion was the unexpected murder of Anthony Ascham, the diplomatic agent of the English régime, early in June 1650 in the capital by six young English royalists. While writing in their defence Hyde presented one of the earliest examples of his case to earn diplomatic support for the exiled Charles II by the Catholic kings of western Europe and the papacy during the coming decade.