LONDON, England (AP) — Prince Philip has had a successful heart procedure at a London hospital and is expected to remain for several days of “rest and recuperation,” Buckingham Palace said Thursday.

The palace said the 99-year-old husband of Queen Elizabeth II “underwent a successful procedure for a pre-existing heart condition at St Bartholomew's Hospital.”

“His royal highness will remain in hospital for treatment, rest and recuperation for a number of days,'' the palace said in a statement.

Philip, 99, has been hospitalised since being admitted to King Edward VII's Hospital in London on February 16, where he was treated for an infection. On Monday he was transferred to a specialized cardiac care hospital, St Bartholomew's.

Camilla, Duchess of Cornwall, said Wednesday that Philip's condition was “slightly improving.”

“We'll keep our fingers crossed," said Camilla, who is married to Prince Charles, eldest son of Philip and the queen.

Philip's illness is not believed to be related to the coronavirus. Both Philip and the monarch received COVID-19 vaccinations in January and chose to publicize the matter to encourage others to also take the vaccine.

Philip, also known as the Duke of Edinburgh, retired in 2017 and rarely appears in public. Before his hospitalization, Philip had been isolating at Windsor Castle, west of London, with the queen.

Although he enjoyed good health well into old age, Philip has had heart issues in the past. In 2011, he was rushed to a hospital by helicopter after suffering chest pains and was treated for a blocked coronary artery.

The longest-serving royal consort in British history, Philip married the then-Princess Elizabeth in 1947. He and the queen have four children, eight grandchildren and nine great-grandchildren.

His illness comes as the royal family braces for the broadcast of an interview conducted by Oprah Winfrey with Meghan, Duchess of Sussex.

Meghan and husband Prince Harry quit royal duties last year and moved to California, citing what they said were the unbearable intrusions and racist attitudes of the British media.

Relations between the couple and the palace appear to have become increasingly strained. On Wednesday, the palace said it was launching a human resources investigation after a newspaper reported that a former aide had accused Meghan of bullying staff in 2018.

In a clip from the pre-recorded Winfrey interview, released by CBS, Winfrey asks Meghan how she feels about the palace “hearing you speak your truth today?”

“I don't know how they could expect that after all of this time we would still just be silent if there was an active role that the firm is playing in perpetuating falsehoods about us,” the duchess says.

“The Firm” is a nickname for the royal family, sometimes used with affection and sometimes with a note of criticism.