 With the Protestant Reformation, the Papacy required all Roman Catholic rulers to consider Protestant rulers as heretics, thus making their realms illegitimate under customary international law.Consequently, Europe's Catholic monarchs considered Ireland a feudal fief of the Papacy, to be granted to any Catholic sovereign who managed to secure the recently-established Kingdom of Ireland from the control of its Protestant monarchs.Paul IV issued a papal bull in 1555, "", recognising Philip and Mary as King and Queen of England and its dominions including Ireland.