London, UK - British head of state, King Charles III, will make a limited return to public duties next week after doctors said they were "very encouraged" by the progress of his treatment for cancer.

His first engagement with Queen Camilla would be at a cancer treatment center on Tuesday. The couple will also host Emperor Naruhito and Empress Masako of Japan for a state visit in June.

The announcement follows a difficult spell for the royal family after both Charles (75) and his 42-year-old daughter-in-law, Kate Middleton, revealed that they had cancer.

Announcing Charles's limited return, a Buckingham Palace spokesperson said it was "too early to say" how much longer his treatment would continue.

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But they noted that his medical team was "very encouraged by the progress made so far and remain positive about the king's continued recovery."

"The pacing of the king's program will be carefully calibrated as his recovery continues, in close consultation with his medical team," the spokesperson added.

The king and Queen Camilla will host the Japanese royal couple at Buckingham Palace in late June, the palace said, confirming reports in the Japanese media last month. The Japanese royals both attended the state funeral of Charles's mother, Queen Elizabeth II, in September 2022, in their first overseas trip after the emperor's enthronement.

An earlier state visit that had been planned for early 2020 had to be postponed because of the coronavirus pandemic.

Neither Charles nor Kate has disclosed the exact type of cancer they are suffering from.

Charles was just 17 months into his reign when the palace announced in early February that he had cancer and would be pausing all public-facing engagements as he began treatment.

The king has continued with behind-the-scenes work holding some in-person meetings and increasingly attending official events.

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He made his most high-profile appearance over the Easter weekend, attending a Sunday church service at Windsor Castle, west of London.

"His Majesty is greatly encouraged to be resuming some public-facing duties and very grateful to his medical team for their continued care and expertise," the palace spokesperson said.

Having both Charles and Kate simultaneously fight serious illness has created an unprecedented crisis in modern times for the British monarchy, with a lack of senior royals available for public duties.

The family would previously have been able to rely on Prince Harry – the king's younger son – to help out, but he and his American wife, Meghan Markle, quit the royal front line in 2020. They now live in California and have been largely estranged from the family following an acrimonious split.

The visit by Japan's royals will be the couple's second international goodwill visit abroad since the Emperor's enthronement. They visited Indonesia last year.

Japanese media reports last month said the couple may visit the University of Oxford, where they both studied at different times.

The couple is also expected to have a luncheon with British Prime Minister Rishi Sunak and his wife, Akshata Murty, according to the reports.