Queen Elizabeth II's 99-year-old husband Prince Philip on Monday left the private London hospital where he had spent nearly two weeks to have heart tests and treatment at another hospital, Buckingham Palace said.

Royal officials said the Duke of Edinburgh, as he is formally known, was taken from King Edward VII's hospital to the state-run St Bartholomew's Hospital in the City of London.

Doctors there "will continue to treat him for an infection, as well as undertake testing and observation for a pre-existing heart condition", they added.

"The Duke remains comfortable and is responding to treatment but is expected to remain in hospital until at least the end of the week."

Philip was admitted to King Edward VII's hospital on February 16 as a "precautionary measure" and on the advice of his doctor, after feeling unwell.

An ambulance leaves the King Edward VII hospital where the husband of Queen Elizabeth, Prince Philip, has been hospitalised since February 16
An ambulance leaves the King Edward VII hospital where the husband of Queen Elizabeth, Prince Philip, has been hospitalised since February 16 AFPTV / Arman SOLDIN

But the palace was quick to point out that his admission was not related to Covid-19, and later said he was being treated for an undisclosed infection.

He and the queen, 94, both had the first dose of a Covid vaccination on January 9 because of their age, which puts them in one of the most vulnerable categories.

An ambulance was seen leaving the King Edward VII's hospital late morning on Monday, driving off past banks of photographers and camera crews.

But a police van -- and tinted windows in the ambulance -- blocked sight of who was inside the vehicle, which left from a rear entrance.

Umbrellas were also held up to conceal the gap between the ambulance and the hospital doors.

An ambulance leaves from the rear entrance of King Edward VII's Hospital in central London, where Britain's Prince Philip, Duke of Edinburgh had been staying after being admitted on February 16
An ambulance leaves from the rear entrance of King Edward VII's Hospital in central London, where Britain's Prince Philip, Duke of Edinburgh had been staying after being admitted on February 16 AFP / Tolga Akmen

Philip turns 100 on June 10 and his already lengthy stay in hospital has raised concerns because of his age, even though he was said to have been comfortable and responding to treatment.

His youngest son, Prince Edward, said last week his father was feeling "a lot better" and was looking forward to returning home.

He thanked members of the public for sending messages of support.

Last Monday, Philip's grandson, Prince William, said the duke was "OK" and being closely monitored by medical staff.

Two days earlier, William's father and Philip's eldest son, heir-to-throne Prince Charles, visited him in hospital but made no comment afterwards.

Philip was able to walk into the hospital unaided when he first was first admitted and arrived using private transport, rather than an ambulance, a source said at the time.

The former naval officer was treated at the same hospital in August 2012 after a recurrence of a bladder infection that laid him low during the queen's diamond jubilee celebrations.

The previous year, he had a stent fitted after suffering a blocked coronary artery.

Barts Heart Centre is Europe's largest specialised cardiovascular service, according to the hospital's website.

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