Duchess Camilla gave an update on her father-in-law's condition two days later when she stepped out to a vaccination centre in Croydon, England, saying the Royal Family are all thinking of the 99-year-old.
"The Duke of Edinburgh yesterday underwent a successful procedure for a pre-existing heart condition at St Bartholomew's Hospital", the palace said, using Philip's formal title.
Philip's current stay in hospital is now his longest ever, raising fears for his health because of his advanced age.
Four days later he was visited by son Prince Charles, who made a 200-mile round trip from Highgrove and stayed 30 minutes.
Royal author Penny Junor claims that airing the interview while Prince Philip remains hospitalized may reflect poorly on the Sussexes.
It was later revealed the duke was being treated for an infection while at King Edward VII Hospital in Central London before he was transferred earlier this week to St Bartholomew's Hospital in London for further treatment.
This is the longest amount of time he has spent in hospital since June 2013 when he had an exploratory operation on his abdomen.
William said he was in good hands and being closely monitored.
It means the Queen will have been parted from her husband of 73 years for at least three weeks.
He has been a constant presence at the side of the monarch, who has referred to him as her "strength and stay".
Philip's illness is not believed to be related to the coronavirus.
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. She spoke to Finance Minister Rishi Sunak ahead of the Budget presentation.
The couple have given an interview to the U.S. chat show host Oprah Winfrey, which is due to be aired on Sunday and expected to add to existing tensions. The BBC will air a special programme to mark this, while rival independent network ITV will show the Oprah interview.