The British monarch visited a cancer hospital Tuesday in London, where he was joined by his wife, Queen Camilla -- who has taken up a number of additional royal duties amid the king's health struggles.

Together, the royal couple mingled with medical specialists and patients at the University College Hospital Macmillan Cancer Centre, discussing the importance of detecting cancer early.

The King also stopped by the center as the new Patron of Cancer Research UK ... a position taken on from his late mother, Queen Elizabeth II.

The couple noted on Instagram after their visit ... "Wishing the very best to all those continuing cancer treatment on their path to recovery."

This outing marks the first public engagement since King Charles announced his cancer diagnosis back in February.

Remember, Buckingham Palace confirmed Prince William and Prince Harry's father was undergoing treatment after cancer was detected while receiving treatment for an enlarged prostate. However, the palace specified the king was not diagnosed with prostate cancer.

There were reports last week that Charles cancer battle was not going well, and the Palace was preparing funeral plans ... just in case. The Palace did not respond to that report, but did say the King would be back on the job shortly.

While KC took a step back for the last several weeks, he reportedly met with a number of small groups ... even stepping out to greet fans of the royal family before a church service on Easter Sunday.

Of course, the King isn't the only member of the British royal family battling cancer -- his daughter-in-law, Kate Middleton, announced in March she had been diagnosed with cancer after undergoing abdominal surgery.