(LONDON) — Britain’s Prince Philip had a “successful procedure” at a London hospital on Wednesday for a pre-existing heart condition, according to Buckingham Palace.

The 99-year-old Duke of Edinburgh “will remain in hospital for treatment, rest and recuperation for a number of days,” the palace said in a statement Thursday.

Philip was transferred to St. Bartholomew’s Hospital in east London on Monday from King Edward VII Hospital in central London, where he was admitted on Feb. 17 for treatment of an infection. Buckingham Palace had said that “doctors will continue to treat him for an infection, as well as undertake testing and observation for a pre-existing heart condition.”

“The Duke remains comfortable and is responding to treatment but is expected to remain in hospital until at least the end of the week,” the palace said in a statement Monday.

St. Bartholomew’s Hospital is located further away from Windsor Castle, a royal residence in the English county of Berkshire where Philip had been staying with his wife, Queen Elizabeth II, but is a larger facility that specializes in cardiovascular treatment, according to the hospital’s website.

While Philip is hospitalized in London, Queen Elizabeth remains at Windsor Castle, where the couple have been staying for most of the coronavirus pandemic. They celebrated their 73rd wedding anniversary in November.

Philip, who will turn 100 in June, was initially taken by car from Windsor to King Edward VII Hospital in London for what Buckingham Palace described as a “precautionary measure” after the duke reported feeling unwell. His illness is not COVID-19-related, a royal source told ABC News.

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