Harry flies out as William fills royal void during King Charles cancer treatment

With Charles, 75, undergoing cancer treatment following Monday's announcement and William's wife Catherine recovering from abdominal surgery, the heir to the throne found himself thrust back to the frontline of royal duties.

Charles's eldest son, William had 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 for an operation.

But on Wednesday the 41-year-old prince was back on duty, hosting an investiture ceremony at Windsor Castle, west of London, for citizens being recognised for their community work and other good deeds.

It had been three weeks since he last appeared at a major royal event.

Later Wednesday, William thanked the public for their "kind messages" before attending a London Air Ambulance fundraising gala.

"We really appreciate everyone's kind messages," he told reporters as he arrived for the charity gala, where he is due to make a speech.

At the same time, Harry arrived back at Heathrow airport for an expected flight back to the United States, around 24 hours after he jetted in.

The prince, dressed casually in jeans, a T-shirt and jacket, was pictured by The Sun daily arriving at the VIP Windsor Suite at Heathrow's Terminal 5.

Charles, who left London on Tuesday for his Sandringham residence in eastern England, will meanwhile hold his weekly meeting with Prime Minister Rishi Sunak by telephone for a change.

"We have agreed with the palace in this specific instance to confirm that they will be speaking on the phone later," Sunak's spokesman said.

'Deep rift'

William is expected to take on some of his father's duties while he undergoes treatment, alongside Charles's sister Princess Anne and his wife Queen Camilla.

Buckingham Palace has not specified the type of cancer the monarch has, although it is understood not to be prostate cancer and Sunak has said it was "caught early".

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

Duke of Sussex Harry's return sparked speculation it could serve as a catalyst to heal the family tensions that have blighted Charles's reign.

He quit royal duties in 2020 and relocated to California where he now lives with his American wife Meghan Markle and their two young children.

The prince has repeatedly aired his complaints about the way he feels he and his wife were mistreated during their time as working royals, culminating in January 2023 with his autobiography "Spare".

Royal commentator Richard Fitzwilliams described the rift between Harry and his brother, as well as the rest of the royal family, as "very deep".

'Pressure on William'

The family's health problems have highlighted the dangers of Charles's plans for a so-called "slimmed down" monarchy.

The departure of Harry and Meghan to California had already left the "Firm", as the Queen called it, depleted in numbers.

Then last month, it was announced that Charles would be hospitalised for a benign prostate condition -- not linked to his cancer diagnosis -- and that Catherine and William would be unavailable for royal duties.

That left 76-year-old Camilla as the most visible face of the royal family, with support from Anne.

Citizens expressed sympathy for William, whom they noted now faced the double burden of maintaining his family life with extra 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 on Tuesday.

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 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."