The King is back in London for what is expected to be further treatment for his cancer diagnosis.
The monarch and Queen Camilla took a helicopter from their private home in Sandringham to Buckingham Palace, then were driven to Clarence House nearby.
The palace announced last week that the 75-year-old was diagnosed with an unspecified form of cancer and had commenced treatment for it.
King Charles delivered his first message since the diagnosis over the weekend, thanking well-wishers and praising organisations which support cancer patients.
However, he did not elaborate on what kind of cancer it was, the type of treatment he was having, or what stage the cancer was at.
His diagnosis comes following treatment in a private London hospital for an enlarged prostate, although the palace said he does not have prostate cancer.
The royal has been advised by doctors to postpone his public-facing duties while he undergoes treatment.
It was also revealed on Wednesday that the King would hold his weekly audience with Prime Minister Rishi Sunak by phone rather than in person, although it was unclear if this was a one-off.
Meanwhile, the Queen has been carrying out her royal diary of engagements and last week said her husband was doing "extremely well under the circumstances".
Both arrived in the capital as rain fell and the King was seen waving to the public.
He was also spotted smiling as he attended church in Norfolk on Sunday morning
Prince William may step in to represent his father at events and it has been reported he and his family are spending half-term at their Norfolk home Anmer Hall, which is on the King's Sandringham estate.