In February, the palace revealed that the 75-year-old king had been diagnosed with an unspecified form of cancer detected in tests after a corrective procedure for an enlarged prostate.
Although Charles continued with official state business, the diagnosis led him to postpone public engagements to begin treatment and rest.
"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," a Buckingham Palace representative said.
"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."
Although it was too early to say how much longer his cancer treatment would last, the representative said his doctors were "very encouraged by the progress made so far and remain positive about the King's continued recovery".
Brilliant news to end the week! — Rishi Sunak (@RishiSunak) https://t.co/icGXxS0TUBApril 26, 2024
No further details about his condition or his treatment were given, in line with the usual stance on medical privacy.
While pictured and filmed carrying out some official duties in private, Charles's only public appearance came last month when he greeted well-wishers in an impromptu walkabout after an Easter church service in Windsor, raising hopes that his health was improving.
United Kingdom Prime Minister Rishi Sunak responded to the news of the King's return to public duties, saying on social media site X: "Brilliant news to end the week!"
To mark his return, Charles and his wife Queen Camilla will visit a cancer treatment centre in London next Tuesday, the palace said.
It was also confirmed that the Japanese Emperor Naruhito and his wife Empress Masako would pay a state visit in late June.
However, Charles will not carry out his usual summer program and his plans will be crafted in consultation with his medical team to minimise risks to recovery, the palace said.
The King's absence has coincided with news that his daughter-in-law Kate, wife of his son and heir Prince William, was undergoing preventative chemotherapy after tests following major abdominal surgery revealed cancer had been present.
The Princess of Wales, often known by her maiden name Kate Middleton, will herself only return to public duties when her medical team say she is well enough to do so.
Charles's health scare came less than 18 months into his reign after he succeeded from his mother, the late Queen Elizabeth, and less than a year since his coronation, the UK's biggest ceremonial event for seven decades.
"As the first anniversary of the coronation approaches, their majesties remain deeply grateful for the many kindnesses and good wishes they have received from around the world throughout the joys and challenges of the past year," Buckingham Palace said.
