A leading Protestant group accused King Charles III of betraying his coronation oath after he prayed alongside Pope Leo XIV during a historic Vatican visit, the first by a reigning British monarch since the Reformation.

The Orange Order said the King’s actions undermined his promise to defend the Protestant faith.

Senior officials from the Orange Order, a Protestant fraternal organisation founded in Northern Ireland in 1795, wrote to King Charles III after his ecumenical service with Pope Leo XIV in the Sistine Chapel on 23rd October 2025.

According to The Orange Standard, the grand masters of Ireland, England and Scotland urged the monarch “to reflect upon the solemn commitments of his coronation oath and the promises he made before God”.

The event marked the first time in nearly five centuries that a British monarch had joined a pope in prayer. The Orange Order said the act blurred the historic Protestant foundations of the United Kingdom, reminding members to “remain steadfast in the Reformed faith, even in the face of opposition”.

A lodge in Markethill, County Armagh, issued an open letter accusing the King of appeasing both Roman Catholicism and Islam, writing that “an Englishman’s word was his bond” but the oath had been “watered down.”

Comparing Charles to his late mother, the group said Queen Elizabeth II had upheld a strong Protestant witness, warning that the King’s interfaith approach reflected Britain’s “spiritual decline.”

The letter concluded: “We pray that God will indeed save the King, from himself.”