London CNN  — 

Prince Philip, the 99-year-old husband of Queen Elizabeth II, underwent a medical procedure for a heart condition on Wednesday, Buckingham Palace said in a statement Thursday.

“The Duke of Edinburgh yesterday underwent a successful procedure for a pre-existing heart condition at St Bartholomew’s Hospital,” the statement read. “His Royal Highness will remain in hospital for treatment, rest and recuperation for a number of days.”

Prince Philip was first admitted to King Edward VII Hospital in London on February 16 “after feeling unwell.” The Palace later confirmed he was being treated for an infection.

On Monday, he was transferred to St. Bartholomew’s Hospital, also in London, for continued treatment of the infection and what the Palace said would be testing and observation for a pre-existing heart condition.

St. Bartholomew’s specializes in cardiac care, according to the hospital’s website, which bills it as “Europe’s largest specialised cardiovascular service.”

Camilla, Duchess of Cornwall, said Wednesday that Philip’s condition was “slightly improving” after his transfer, despite his treatment hurting “at moments,” according to PA Media.

“We keep our fingers crossed,” Camilla added of her father-in-law, according to PA.

Both Philip and the Queen have received at least one dose of a Covid-19 vaccine.

They have spent most of the past year at Windsor Castle, having moved away from Buckingham Palace during the first wave of the Covid-19 pandemic in spring 2020.

The prince stepped back from public life in 2017 and has been taken to the hospital several times in recent years. In December 2019, he received hospital treatment for a pre-existing condition.