LONDON, UNITED KINGDOM- With his father King Charles III undergoing treatment for cancer and his wife recovering from surgery, Britain's Prince William will return to royal frontline duties on Wednesday.

The king's shock cancer diagnosis, announced on Monday, and Catherine's abdominal operation have left William shouldering a heavy royal burden.

William, 41, Charles's eldest son and heir to the throne, postponed public engagements to care for his wife, the Princess of Wales, and their three children after she was admitted to hospital on January 16.

But he will be back at work on Wednesday, handing out honours awarded to citizens for good deeds at Windsor Castle before attending the London Air Ambulance annual fundraising gala in central London.

He is also expected to take on some of his father's duties while he undergoes treatment, with fellow senior royals Princess Anne and Charles's wife Queen Camilla helping to share the load. 

Buckingham Palace has not specified the type of cancer afflicting the 75-year-old monarch, although it is understood not to be prostate cancer.

UK Prime Minister Rishi Sunak said it had been "caught early".

The diagnosis comes just 17 months into his reign following the death of his 96-year-old mother, Queen Elizabeth II, on September 8, 2022.

 'Very deep' rift 
Adding to the drama, the king's estranged son Prince Harry flew into the UK from his US home on Tuesday.

Shortly afterwards, a relaxed-looking Charles was seen leaving his Clarence House residence in London for Sandringham, his country estate in eastern England.

The news sparked immediate speculation it could serve as a catalyst to heal the family tensions that have blighted the start of Charles's reign.

Royal commentator Richard Fitzwilliams, however, described the rift between Harry, also known as the Duke of Sussex, and the rest of the royal family as "very deep".

Harry has a particularly fractious relationship with brother William.

People expressed sympathy for William, who they noted now faced the double burden of maintaining his family life with official duties.

"He's got a hard job because his wife is poorly at the moment, so that's an added pressure on poor William, but I'm sure that he will cope," pensioner Sue Hazell told AFP outside Buckingham Palace, another of the king's London homes, on Tuesday.

Kate is expected to be out of action until at least March 31, her Kensington Palace office said.

Officials have not given details of her surgery except to say it was not linked to cancer.

Canadian tourist Sarah Paterson, a 44-year-old entrepreneur, said that William must be "beside himself" given the recent deaths of his grandfather and his grandmother, along with the health problems faced by his father and his wife.

But she said she was "1,000 percent" confident that William would be a good stand-in, adding: "I think he'll probably be king sooner than he hoped."

The King won plaudits for being open about his condition, a break from tradition for a family that is renowned for being extremely discrete about personal health issues.

"It's a great image to have someone who speaks about his problems like this," Italian tourist Giacomo Lanza, 22, told AFP.