The Duke of Edinburgh is “OK” after spending a sixth night in hospital, the Duke of Cambridge has said.
Speaking on a visit in Norfolk, Prince William also told reporters that doctors were “keeping an eye” on his 99-year-old grandfather.
Prince Philip was admitted to the King Edward VII’s hospital in London last week as a precaution.
The exact reason for his admission has not been disclosed but his stay is not related to coronavirus.
A Buckingham Palace source said on Friday that it was likely Prince Philip would stay in hospital into this week.
He was visited by his son, the Prince of Wales, on Saturday.
A palace source previously said that the duke, who turns 100 in June, had walked into the hospital in Marylebone unaided.
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He had been feeling unwell for a few days and was admitted as a precaution on the advice of his doctor.
Both he and the Queen, 94, received Covid-19 vaccinations last month.
The couple, who celebrated their 73rd wedding anniversary last November, have been spending lockdown at Windsor Castle with a small household staff.
Prince Charles, 72, spent about 30 minutes at the hospital visiting his father on Saturday afternoon.
A Clarence House spokesman said he returned to his Highgrove residence after the visit.
Prince William was asked about the duke’s health during a visit to a Covid-19 vaccination centre in the King’s Lynn Corn Exchange, in Norfolk. It is near Anmer Hall, where the Duke and Duchess of Cambridge have been staying with their children during lockdown.
Other members of the Royal Family have also continued with their official duties in the past few days.
The Queen knighted a royal aide during a private socially-distanced ceremony at Windsor on Thursday.
Meanwhile, Prince Charles and the Duchess of Cornwall unveiled a plaque to thank NHS workers during a visit to the Queen Elizabeth Hospital in Birmingham last week.
Prince Philip has received treatment for various health conditions over the years, including a blocked coronary artery in 2011, a bladder infection in 2012 and exploratory surgery on his abdomen in June 2013.