King Charles joined over 500 worshippers at an Advent Service and Christmas Reception at the Coptic Orthodox Church Centre in Hertfordshire on Tuesday.
After the service, His Majesty spent time meeting young volunteers from the church and was given a Christmas letter by a six-year-old girl wishing him "Happy Holidays". The Sun's religious correspondent Matt Wilkinson reported that the King replied, "I'm very touched, thank you".
The Cathedral of St George, near Shephalbury Manor, is the central venue for the nearly 40,000 members of the Coptic Orthodox church in the UK. The historic denomination, which has its roots in Egypt, originated in the earliest days of Christianity. Many of its churches there are centuries old.
The King's visit was part of continued efforts to encourage interfaith dialogue and a greater understanding of different religions in Britain and abroad.
The church described the reaction to the event in a post on X, formerly known as Twitter.
"A day filled with jubilation and excitement as His Majesty The King @RoyalFamily welcomed by @BishopAngaelos visits over 500 members of The Coptic Orthodox community @CopticDiocese in the United Kingdom and over 100 official, interfaith and ecumenical guests who joined them.
Several church leaders from other denominations were invited to join in the occasion."
The Bishop of Southwark, Rt Rev Christopher Chessun, was present, and the Bishop of St Albans was among those who greeted the King on his arrival. Commenting on the event the following day, the Rt Rev Alan Smith told Premier: "King Charles has always been a passionate supporter of Christians of all denominations, so it was wonderful that he paid a visit to the Coptic Cathedral in Stevenage yesterday. Our Coptic brothers and sisters have faced much opposition and suffering over the years, so they greatly appreciate the support that he continues to give to the persecuted church.
"It was also an encouragement to the people of Stevenage that the King chose to make this visit in the busy lead up to Christmas."
General Secretary of Churches Together, Mike Royal, who played a role in the King's Coronation service, was also there. He wrote on social media:
"Delighted to join H. E Archbishop @BishopAngaelos at the Coptic Orthodox Church Cathedral for a Christmas Service and Reception with His Majesty King Charles III alongside dear ecumenical friends… #Orthodox"
A 15-minute service included prayers, gospel readings and the Orthodox Creed.
After unveiling a plaque, the King told the congregation he had the "greatest admiration for the Coptic community".
"If I may say so, this has been a very special occasion and I want to wish you nothing but a very happy Christmas indeed."
The King concluded his visit by planting a plum tree at the front of the centre. He was seen waving to attendees as he left.