Prince Harry reportedly was not aware that his father, King Charles III, had been kept in hospital for observation after suffering temporary side effects in his ongoing cancer treatment.

The reigning monarch is understood to have been receiving treatment on Thursday when he started to display symptoms linked to side effects.

His calendar was quickly amended, with multiple engagements postponed.

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However, amidst the swift changes to the monarch’s plans and the issuing of an official statement from Buckingham Palace, sources claim Harry was not contacted.

A source told The Sun that Harry, they understood Buckingham Palace did not want to alarm Harry, adding the Prince is reportedly lonelier than ever.

“First he was a spare to William, now he’s increasingly looking like a spare to Meghan — and it’s not a great look,” the source said.

“He misses his family terribly, but no one is speaking to him any more,” claimed another.

“He just wants to go for a beer with the guys, but his only friends are just the husbands of Meghan’s friends.”

Charles cancelled a trip to Birmingham on Friday to prioritise his recovery and is back at Clarence House.

Buckingham Palace said in a statement: “Following scheduled and ongoing medical treatment for cancer this morning, the King experienced temporary side effects that required a short period of observation in hospital.

“His Majesty’s afternoon engagements were therefore postponed.

“His Majesty has now returned to Clarence House and as a precautionary measure, acting on medical advice, tomorrow’s diary program will also be rescheduled.”

Hours after news broke, the world saw King Charles out in high spirits, smiling and waving at the public in London, keen to put concerns at ease.

Charles was diagnosed with an undisclosed form of cancer in February 2024 and returned to public-facing duties in April despite still undergoing weekly treatment.

- With AP