The King’s Christmas message will focus on the efforts of healthcare workers following a year that saw Charles and the Princess of Wales treated for cancer.
The King will also use his annual address to the nation to hail communities who came together in solidarity in the aftermath of rioting, following the fatal Southport stabbings of three young girls.
The message was recorded at Fitzrovia Chapel, a former sacred space of the demolished Middlesex Hospital where Diana, Princess of Wales opened London’s first dedicated Aids ward.
It is understood the speech will reflect on international, national and personal challenges and how they can be overcome by communities supporting one another.
Carla Whalen, chair of the Fitzrovia Chapel Foundation’s board of trustees, said about the filming: “I assume that this space being one of calm reflection, but also thinking about health, about care, about the medical profession, would make it a pretty apt choice.”
In keeping with the King’s desire to go out into the community, he tasked the team organising the broadcast to find a site away from the royal estate.
He gave them a criteria the building must fulfil, including having health connections, a strong community presence and providing all faiths and none a place of solace and reflection.
They discovered the Grade II* listed building in central London which has Byzantine-inspired architecture and is richly decorated in a Gothic revival style featuring marble and more than 500 stars in a gold leaf ceiling.
Charles picked the chapel without visiting and was left “absolutely bowled over” by its beauty, said a source.
Ms Whalen said of his arrival: “He was pretty surprised and kind of delighted, as far as I can tell, from coming in and discovering it.
“He was very interested in the marble, there’s 40 types of marble here and lots of different designs and he wanted to learn about the history of the chapel and some of the people who are commemorated here.”
Charles recorded his message on December 11, one of the rare times a building outside the royal estate has been used, with the late Queen recording her message at Southwark Cathedral in 2006 and at Combermere Barracks in Windsor three years earlier.
Speaking about the King’s criteria for the building, the source said: “Obviously it made sense it had some form of health connection, because that of course has been a dominant theme for the family in all kinds of different ways.
“Secondly and equally importantly, that it should speak in some way of bringing communities together… thirdly of course it does help if it looks rather beautiful and is a place of spiritual solace and reflection.”
The source added the King was “absolutely bowled over by how beautiful it was and how special a place it is”.
Charles announced in February he had been diagnosed with cancer, following treatment for an enlarged prostate, and the following month the Princess of Wales revealed she was undergoing a course of chemotherapy, since completed, and she has made a partial return to public duties.
The King’s ongoing treatment is understood to be heading in a positive direction, and after initially postponing all public-facing engagements he returned to events in April, carried out a major southern hemisphere tour in October and his diary in the run-up to Christmas appears very similar to his pre-cancer period.
Fitzrovia Chapel, designed by architect John Loughborough Pearson with work beginning in 1891, is a few minutes’ walk from Oxford Street, Europe’s busiest shopping destination, but offers a tranquil space and is a popular wedding venue and arts exhibition site.
It was used by patients, medical staff and the public visiting the Middlesex Hospital, which closed in 2006 and had stood on the site since 1755 before being demolished in 2008.
Following the broadcast the Christmas tree, a living specimen covered with sustainable decorations, was donated to Croydon BME (Black and Minority Ethnic) Forum and Macmillan Cancer Support’s Can You C Me? project that strives to tackle ethnic inequalities in cancer care.
It will be placed in the Royal Trinity Hospice in Clapham, south London, which has the Queen as its patron.