The King paused to chat to members of the public as he walked to church on the Sandringham estate in Norfolk on Sunday.
Several dozen well-wishers turned out to see Charles, 75, as he strolled to the service at St Mary Magdalene Church.
Members of the public were invited into the paddock near the church – as they are on Christmas Day – on the warm July day.
The King – who is continuing to receive treatment following a cancer diagnosis – wore a grey suit, purple tie and brown shoes.
The sun shone as he made the short journey, of a few minutes on foot, from Sandringham House to the church.
Charles, who was not joined by Camilla, briefly spoke with members of the public before being greeted by the Rev Canon Dr Paul Williams.
