“His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties,” the palace said in a statement.

“He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible,” the palace added.

The king is expected to continue to receive his “red boxes” containing documents from the government that the monarch must review. He is not expected to appoint a “counsellor of state,” or another senior member of the royal family whom he can delegate his duties to. It was not clear whether he might continue his regular meetings with the prime minister via video call, as Queen Elizabeth II did during the pandemic.

Prime Minister Rishi Sunak posted on X, formerly Twitter: “Wishing His Majesty a full and speedy recovery. I have no doubt he’ll be back to full strength in no time and I know the whole country will be wishing him well.”

The royal family was already shorthanded, with Catherine, Princess of Wales, recovering from abdominal surgery and Prince William, heir to the throne, taking a step back from royal duties to care for his wife and children. William is expected to make a public return later this week. A palace spokesperson said that Queen Camilla will continue with a “full program” of public duties.

Prince Harry spoke with the king about his cancer diagnosis and will travel to Britain to see his father in the coming days, according to a person in the office of the Duke and Duchess of Sussex.

Well wishes poured forth. The leader of Scotland, First Minister Humza Yousaf, said he prayed for “a speedy recovery” for the king, adding that his thoughts were also directed to the royal family “at what I know will be a worrying time.”

Charles and Camilla were photographed Sunday arriving together for church service at St. Mary Magdalene Church in Sandringham. Buckingham Palace said he returned to his London home, Clarence House, Monday morning to “commence treatment as an outpatient.”

The palace is traditionally tight-lipped about the health of the monarch. But a spokesperson said the king wanted to make his diagnosis public “to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer.”

The palace noted that as Prince of Wales, Charles was a patron of cancer-related charities and “has often spoken publicly in support of cancer patients, their loved ones and the wonderful health professionals who help care for them.”

The palace statements to the public and the media did not contain the specificity of the announcement just a few weeks ago that Charles would undergo a “corrective procedure” for an enlarged prostate. In that instance, the written statement provided a link to Britain’s National Health Service, which explained that the condition can affect how a man urinates and is common to men over 50.

Camilla was asked last week how her husband was recuperating, and she replied, “He’s getting on, doing his best.”

In its statement Monday about the cancer treatment, the palace said Charles is “grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure.”

British royal family members in recent times have enjoyed impressive longevity. Charles’s grandmother, the Queen Mother, lived to 101. His father, Prince Philip, died at 99 — the official cause was “old age.” His mother, Queen Elizabeth II lived to 96. “Old age” was also listed as the cause.

Before Elizabeth’s death, the palace only noted that she was suffering from “mobility” issues to explain her use of a cane and her scaled-back schedule.

Her father, Charles’s grandfather, King George VI, died relatively young — at age 56 in 1952, after failing to recover from a lung operation.

Charles spent more than 70 years as heir apparent. At 73, he was the oldest person to ascend to the British throne. During that long wait, he led an active life. He was a competitive polo player until 57. He is a vigorous walker, and an organic gardener who likes laying his own hedges.

Charles believes homeopathic and herbal remedies can play a supporting role alongside modern medicine.

He is also known to enjoy whisky and fine wines. He told a group of nurses that he was never much of a smoker. He mostly avoids meat, enjoys fish and eats vegetarian one day a week. For breakfast, Town and Country magazine reported that he has a bowl of muesli with some fruit, “often some plums from the garden that have been lightly poached.”