Lattery Purple Heroes in Markethill has published the correspondence sent to one of Charles’s most senior officials.
The letter notes how some priests “absolved the sins’ of republicans who killed members of the Orange institution and others.
It comes after Orange Order leaders wrote to the King urging him to “reflect on his coronation oath”.
Last month Charles became the first reigning English monarch to pray publicly with a pope since Henry VIII.
However, there was criticism from some sections of unionism.
This week the Orange Standard, the institution’s official publication, reported that “many members of the Orange family will have been disappointed” by the meeting.
It stated: “The Grand Masters of Ireland, England and Scotland have jointly written privately to His Majesty to encourage him to reflect upon the solemn commitments of his coronation oath and the promises he made before God.”
Now, Lattery Purple Heroes LOL 222 has released a copy of a letter, via its Facebook site, that its members sent to Sir Clive Alderton, the King’s principal private secretary.
It states: “After much deliberation and with the greatest of regret, we as a private Orange Lodge, part of the Grand Orange Lodge of Ireland and loyal to the Crown, find ourselves in the position of having to write in sad criticism in regards to the joint prayer service of His Majesty King Charles the Third and Robert Francis Prevost, current Pope Leo and Bishop of the Roman Catholic Church.
“His Majesty took a Coronation Oath to be Defender of the Protestant Faith. There was a time when an Englishman’s word was his bond but sadly we have seen that oath watered down, first in his appeasement of Islam and now with bending the knee to the head of a church whose heretical priests ‘absolved the sins’ of those who murdered members of our Institution, our friends and family.
“Our society is one already at odds with the notion of monarchy of which it and His Majesty hold a privileged position.
“Sadly, the United Kingdom, whose strong Protestant Faith witnessed by Her Majesty Queen Elizabeth the Second, once a beacon to the world, has become a country the world no longer respects.
“We cannot understand why His Majesty wishes to alienate further those still loyal to the Crown as he seeks to be a defender of all faiths and not promote the one true Faith.
“Jesus Christ is the Way, the Truth and the Light. A true defender of the Faith should not be embarrassed about saying that, a weak king might.
“We will pray that the King of Kings will not only continue to bless the monarchy but will particularly pray that God will indeed save the King, from himself.”
King Charles III and Queen Camilla with Pope Leo XIV last month. Aaron Chown/PA Wire
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Previously, the Independent Orange Order expressed “great sadness” at the meeting, citing a catalogue of grievances with the “obnoxious” theological position of the Catholic Church, which it said has no biblical basis.
Kyle Paisley, the son of the late DUP founder Ian Paisley, also called on Charles to cancel the engagement or “abdicate” and “let someone else take his place who is a true Protestant”.
A Buckingham Palace spokesperson said at the time that the trip was intended to mark “a significant moment in relations” between both churches, recognise the ecumenical work they have undertaken and reflect the Jubilee year’s theme of walking together as ‘Pilgrims of Hope’.