Buckingham Palace announced on Friday that doctors were sufficiently pleased with the 75-year-old King's response to treatment for the unspecified form of cancer that he would be able to resume some public-facing engagements.
The first of these will be Tuesday's visit to a cancer treatment centre to meet patients and medical specialists.
The palace has also announced Charles and his wife Queen Camilla will host a state visit by the Japanese Emperor Naruhito and his wife Empress Masako in late June.
Charles' health issues began in January when it was revealed that he would be admitted to hospital to have a corrective procedure for a benign enlarged prostate.
The following month, the palace said tests had uncovered the presence of a "form of cancer", but gave no further details beyond saying it did not involve his prostate.
He has rested and undergone treatment for the disease since then, continuing with official state duties in private. He was well enough to greet well-wishers after an Easter church service at the end of March.
Although his diary will be carefully managed to minimise any risks to his health, the palace said he might attend some annual events such as the Trooping the Colour military parade in June, as well as commemorations to mark the 80th anniversary of the World War 2 D-Day landings, also in June.
Charles' illness came less than 18 months after he succeeded his mother Queen Elizabeth II. His nephew Peter Phillips has said the monarch, who is renowned for hard work, had found the limitation imposed by his treatment frustrating.
Also absent has been Charles' daughter-in-law Catherine, Princess of Wales, wife of his son and heir Prince William, who is undergoing preventative chemotherapy after tests in the wake of major abdominal surgery revealed that cancer had been present.
Harry back for Invictus milestone
Prince Harry will return to Britain to celebrate the 10th anniversary of his Invictus Games in May, before joining his wife Meghan on a visit to Nigeria, his spokesperson says.
Harry, the second and youngest son of King Charles, lives in the United States with Meghan, Duchess of Sussex, and their two children after he gave up working as a member of the Royal family in 2020.
He has only returned to Britain on a few occasions since his departure from royal life, arriving for major events such as Elizabeth's funeral in 2022 and his father's coronation in May last year.
His spokesperson said Harry would attend a service at St Paul's Cathedral in London on May 8 to celebrate the Invictus Games, the international sporting event that he founded for military personnel wounded in action.
Harry served as a military helicopter pilot in Afghanistan and Invictus organisers said the service was designed to mark "a decade of changing lives and saving lives through sport".
The Prince was last seen in Britain in February this year for a brief meeting with King Charles after his cancer diagnosis.
