King George V and the Accession Oath

Before 1910, but even after the 1829 Emancipation of Catholics, English monarchs still had to take an extraordinarily insulting anti-Catholic oath before Parliament upon their accession to the throne:

I, A. B., by the grace of God King (or Queen) of England, Scotland and Ireland, Defender of the Faith, do solemnly and sincerely in the presence of God, profess, testify, and declare, that I do believe that in the Sacrament of the Lord's Supper there is not any Transubstantiation of the elements of bread and wine into the Body and Blood of Christ at or after the consecration thereof by any person whatsoever: and that the invocation or adoration of the Virgin Mary or any other Saint, and the Sacrifice of the Mass, as they are now used in the Church of Rome, are superstitious and idolatrous. And I do solemnly in the presence of God profess, testify, and declare that I do make this declaration, and every part thereof, in the plain and ordinary sense of the words read unto me, as they are commonly understood by English Protestants, without any such dispensation from any person or authority or person whatsoever, or without thinking that I am or can be acquitted before God or man, or absolved of this declaration or any part thereof, although the Pope, or any other person or persons, or power whatsoever, should dispense with or annul the same or declare that it was null and void from the beginning"

King Edward VII, George's father, had not wanted to take that oath upon his accession--either before Parliament or at his coronation, but it required an Act of Parliament. As this site notes:

George V in 1910 objected to the wording in the Accession Declaration used since Queen Anne’s reign, which denied the existence of transubstantiation in the Sacrament of the Lord’s Supper. He was also offended by references to invocations to the Virgin Mary and the sacrifice of the Mass as being superstitious and idolatrous. Despite some strong opposition the King succeeded in having all the above deleted and replaced by a more straightforward Declaration: ‘I (name) do solemnly and sincerely in the presence of God profess, testify and declare that I am a faithful Protestant, and that I will, according to the true intent of the enactments which secure the Protestant succession to the Throne of the Realm, uphold and maintain the said enactments to the best of my powers according to the law.’ Each monarch since then, including our current Queen has used that Declaration.

George was following his father's lead; Edward VII once reminded a courtier: “You don’t understand me. I am the King of all the people.” George V was crowned on June 22, 1911.