London (CNN) — King Charles III, who is being treated for an unspecified cancer, returned to public duties on Tuesday with his first official engagement since his diagnosis after his doctors were said to have been “very encouraged” by his progress.

The 75-year-old monarch revealed he was battling cancer in early February and is continuing his treatment as he restarts his public-facing engagements.

The first fresh entry in his diary was a visit to a cancer treatment center in London, where he was expected to meet patients and staff.

The King, who has been patron of Macmillan Cancer Support for nearly three decades, was accompanied by his wife, the Queen. The pair smiled and waved at well-wishers gathered nearby upon arrival before being welcomed to the hospital by medical staff.

Camilla, 76, has been president of cancer care and support charity, Maggie’s since 2008.

The King has largely remained out of the public eye during his treatment so far, apart from an outing on Easter Sunday when he delighted crowds with an impromptu walkabout after attending church with several family members.

Tuesday’s visit to University College Hospital Macmillan Cancer Centre was to reiterate the value of early diagnosis and focus attention on some of the innovative research taking place there.

The King’s outing came as he was announced as the new patron of Cancer Research UK. While at the center, he was due to meet with the organization’s chief clinician, Charlie Swanton, who has led a project called TRACERx, which is focused on lung cancer.

While Buckingham Palace announced on Friday that the British sovereign had been given the green light to return to public duties, it will be a cautious return.

It said that forthcoming events would be adapted where necessary to minimize any risks to his convalescence.

The palace did not specify how many engagements were being added to the King’s diary or whether he would be able to attend his birthday parade in London or the D-Day 80th anniversary commemorations in Normandy in June.

However, it has been confirmed that he will welcome Japan’s Emperor and Empress for a state visit later that month.

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