Officials said at the time that although Charles would be stepping back from public-facing events, he would continue to “undertake state business and official paperwork as usual”.

It has been reported that Charles was a “little frustrated” by the impact the diagnosis had on royal plans so early into his reign but was otherwise he is “in his usual good form”. Next week will mark one year since his coronation at Westminster Abbey.

Since the princess and the King’s cancer diagnoses, palace source say that the monarch has “remained in the closest contact with his beloved daughter-in-law throughout the past weeks”. The bond between the King and Kate became official last week when he appointed her a Royal Companion of the Order of the Companions of Honour.

The King’s planned visit to the cancer centre next week will be the first in a number of external engagements the monarchs will undertake in the weeks ahead, which will also include hosting the Emperor and Empress of Japan for a State Visit in June, at the request of UK government.

However, palace sources said each engagement would continually be “carefully reviewed” and managed to reduce any risks to the King’s recovery. It is understood the palace has no plans to share further details of his specific condition or treatment plan at this stage.

"His Majesty’s treatment program will continue, but doctors are sufficiently pleased with the progress made so far that The King is now able to resume a number of public-facing duties," they said.

"Forthcoming engagements will be adapted where necessary to minimise any risks to His Majesty’s continued recovery."

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