He was also announced as patron of Cancer Research UK as he visited the Macmillan Cancer Centre with the Queen.

He takes over the patronage from his mother, the late Queen Elizabeth.

It was the King's first public outing since doctors told him to avoid public-facing duties while undergoing cancer treatment.

He was pictured holding hands with some of the patients at the London centre, part of University College Hospital.

The royals also gave presents to children on their way out.

On Friday, the Palace announced that the King was "greatly encouraged" to be given the green light by doctors to return to some public-facing duties.

However, sources have stressed that despite the welcome news, the King still has cancer and will continue to be treated for the undisclosed form of the disease.

It is hoped that his visit will draw attention to the importance of early diagnosis, as well as the innovative new treatments and research being worked on at the hospital supported by Cancer Research UK.

The monarch, who is also the patron of Macmillan Cancer Support, will meet patients and their families today.

He will also meet the team behind a project called TRACERx, the single biggest investment in lung cancer research by Cancer Research UK which aims to investigate how lung cancer evolves over time and why treatments sometimes stop working.

The King decided to announce he had cancer at the beginning of February.

Since then, cancer charities have praised his openness and the impact it's had on raising public awareness, along with the Princess of Wales also talking about her diagnosis.

Ahead of the visit today, a Buckingham Palace spokesperson said: "His Majesty's treatment programme 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 added: "Forthcoming engagements will be adapted where necessary to minimise any risks to His Majesty's continued recovery."

The King has continued to carry on with his constitutional work behind the scenes and held small meetings inside the palace, including with Prime Minister Rishi Sunak.

At Easter, he made a point of greeting crowds who had turned out to see him attend the church service at St George's Chapel, Windsor, which was seen as a hint that more public-facing engagements could soon follow.

Palace officials continue to plan for a busy summer and autumn of events but will work around the caveat that plans may need to change depending on the King's health and doctors' advice.

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The summer months are always a busy period for the Royal Family with events such as Trooping the Colour, Garter Day, and Royal Ascot.

There is also the prospect of overseas travel towards the end of the year, as Samoa is hosting the biennial meeting of Commonwealth leaders.