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 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.