Prince William has said the Duke of Edinburgh is “ok” and doctors are “keeping an eye on him” in hospital.
The Duke of Cambridge had been visiting a vaccination centre in King’s Lynn, Norfolk, when he spoke about his grandfather’s health.
Prince Philip, 99, has spent a sixth night at King Edward VII Hospital in central London after being admitted last Tuesday “as a precautionary measure”.
A royal source said the reason for the hospital stay was not coronavirus-related.
On Saturday, the Duke of Edinburgh was visited by his son the Prince of Wales, and the pair spent about 30 minutes together.
Sky News understands Prince Charles travelled from Highgrove in Gloucestershire and was visiting because the duke had been in hospital a little longer than expected.
On Friday, it was reported that the Duke of Edinburgh was likely to remain in hospital until later this week for rest and observation, although he was said to be in “good spirits”.
There were no further visits to the duke by family members on Sunday, though police and security cars remained in place at the hospital throughout the day
Heart-shaped balloons and a letter written by a 10-year-old boy from north London, wishing Prince Philip a quick recovery, were tied to the hospital railings.
The duke has been staying with the Queen at Windsor Castle since coronavirus restrictions were first introduced last year.