The Latin title Rex Catholicissimus, Anglicized as Most Catholic King and Most Catholic Majesty, was awarded by the Pope to the Sovereigns of Spain. It was first used by Pope Alexander VI in the papal bull Inter caetera in 1493.
One of the rights of a "Most Catholic" queen – either regnant or consort – is the privilège du blanc, meaning that she may wear white colored garments when meeting the Pope rather than the normal black used by other consorts and heads of state.
The monarchs of other countries have received similar titles from the pope:
- Hungary: Apostolic Majesty (awarded c. 1000)
- France: Most Christian Majesty (awarded c. 1380)
- England: Defender of the Faith (awarded in 1521, revoked c. 1530)
- Germany: Defensor Ecclesiae (Protector of the Church; awarded to Holy Roman Emperors)
- Portugal: Most Faithful Majesty (awarded in 1748)