Mystery surrounds Prince Philip's hospital stay

The Duke of Edinburgh is in hospital this Christmas. Photo / Getty

The 98-year-old Duke of Edinburgh is being "looked after very well but that's all we know", according to his son Prince Charles.

Prince Philip was flown via helicopter to London from Sandringham for observation and treatment for a pre-existing condition, the Sun reported.

Charles spoke to a reporter as he arrived in Fishlake, South Yorkshire, to see the damage severe flooding had caused when it hit the village last month.

"He's all right — once you get to that age, things don't work as well. He's being looked after very well in hospital," he said.

In its statement Buckingham Palace downplayed the Duke's visit to King Edward VIII Hospital, calling it a "precautionary" measure.

The Duke is said to be hoping to make it to his 100th birthday. Photo / Getty

It was also reported by the Mirror that Philip has been seen joking with doctors in the hospital as he aims to recover to spend Christmas at the Queen's side.

The Queen's schedule hadn't changed - she was seen leaving Buckingham Palace for Norfolk to set off on her annual Christmas break at the Sandringham estate.

The Duke's admission to hospital comes after a month of ill health - along with a severe fall.

"The Duke had a bad fall and was confined to bed for a couple of days," a royal source told The Sun.

"He didn't break anything, but it gave everyone a scare. He suffers from gout, which makes him more irritable, and he lost his appetite.

"Those around him were worried as he'd stopped eating and didn't want to go out. But he's a 98-year-old man and this is all very common at this age.

Prince Charles said his father was being looked after but that was all the royal family knew. Photo / Getty

"He's been in good health generally but missed the Queen's Christmas lunch at Buckingham Palace on Wednesday for the first time.

"And for the first time in what feels like centuries he won't be seen shooting anywhere this year, not even on the Sandringham estate which is a great shame."

Another source said the Duke "didn't want any fuss".

"He doesn't want the family coming to see him in hospital.

"He wants to be in and out with minimal disruption to any festive plans and he certainly doesn't want the family to spend time at Christmas traipsing to his sick bed."

In the past he's experienced heart problems, arthritis, bladder infections and abdominal surgery.

The Queen made her yearly trip to the Sandringham estate this week. Photo / Getty

He had a hip replacement in April 2018, recovering just in time for Harry and Meghan's wedding the following month.

Palace sources stressed that the Duke was not taken to hospital by ambulance and that it was a planned visit.

"The admission is a precautionary measure on the advice of His Royal Highness's doctor."

One of the Duke's friends also said that although he'd previously said he didn't want his life to drag on, he was now keen to hit 100.

Buckingham Palace said the Duke's decision in 2017 was not health-related.