The King wished volunteers and members of the public a “Happy Christmas” ahead of attending an Advent service in central London.
Charles met with representatives and beneficiaries of local initiatives before unveiling a plaque at the King’s House community hub in King’s Cross on Thursday morning.
The monarch then greeted the cheering crowds gathered on Pentonville Road outside as he made his way to the nearby Ethiopian Christian Fellowship Church for an advent service.
The visit came just after the first three episodes of Meghan and Harry’s six-part bombshell Netflix documentary were released at 8am.
Charles was joined by Archbishop of Canterbury Justin Welby as well as the Bishop of London Sarah Mullally and Coptic Orthodox Archbishop of London Anba Angaelos as they spoke to volunteers from groups like Growing Hope, Little Haven, Open Doors and the Prison Ministry/London City Mission in King’s House.
The monarch also unveiled a plaque to commemorate his visit, joking: “Are you sure you want a plaque?”
He then told the room: “Can I wish everyone as blessed a Christmas as possible to you all.
“And I’m so impressed by every wonderful things that have happened in every corner of the building and it’s wonderful that you take such trouble and make such a difference to so many people’s lives.
“So I can only thank you, rather inadequately, for that.”
Charles also spoke to Christians Against Poverty (CAP) representative Keilah Gallardo and local Marie Cuss, who the organisation helped to get out of debt.
He discussed a pinboard map that CAP had on display, showing green and white pins indicating their clients in the local area – white for those who are no longer in debt.
The King said: “The aim is for all of them to be white, isn’t it?”
Ms Gallardo told the PA news agency: “He seems to really have an interest in what we are doing. He said that it’s an important issue, especially as it’s a very difficult time that we are living in.”
As Charles left the building, he paused to watch a choir from the local all girls Elizabeth Garrett Anderson school sing “What If” by India Arie in the entrance.
He then stopped to greet crowds of people taking pictures on the street and wished more people a “very Happy Christmas” as he walked to the Ethiopian Christian Fellowship Church for an advent service.
On arrival, Reverend Dr Getachew Zergaw welcomed the King, who could be seen smiling and waving as the congregation stood and applauded.
Charles sang along and tapped his foot as a band played an energetic gospel-style rendition of “Oh Come All Ye Faithful” by the King’s Cross Church band.
The King’s visit came in the immediate wake of the first three parts of the Duke and Duchess of Sussex’s documentary in which the couple covered topics like their early relationship, the media intrusion, Meghan confronting the “formality” of the royal family as an American and Harry growing up without his mother, Diana, Princess of Wales.