Prince William said on Monday that his grandfather, Prince Philip, is "OK" as the 99-year-old royal consort remains in a London hospital for rest and observation.
William was asked about Philip when he visited a coronavirus vaccination centre in eastern England.
"Yes, he's OK, they're keeping an eye on him," William said, and gave a wink.
Philip was admitted to the private King Edward VII's Hospital in London on Tuesday after falling ill. Buckingham Palace said the husband of Queen Elizabeth II was expected to remain in the hospital into this week for a period of "observation and rest".
Philip's illness is not believed to be related to Covid-19. Both he and the Queen, 94, received a first dose of a vaccine against the coronavirus in early January.
Philip, who retired from public duties in 2017, rarely appears in public. During England's current coronavirus lockdown, Philip, also known as the Duke of Edinburgh, has been staying at Windsor Castle, west of London, with the queen.
Philip married the then-Princess Elizabeth in 1947 and is the longest-serving royal consort in British history. He and the queen have four children, eight grandchildren and nine great-grandchildren.
Prince Philip received a visit from his son Prince Charles over the weekend, a trip that was criticised by many given the current restrictions on hospital visits under lockdown laws.
Charles arrived at King Edward VII's hospital over the weekend to visit his 99-year-old father, who was admitted as a "precautionary measure" last week, reports the Daily Mail.
Since photos emerged of a tearful Prince Charles leaving the hospital, the hashtag #princephilip has been trending on Twitter, with many slamming the Prince of Wales' visit amid the lockdown.
"I do hope Prince Phillip gets better but why was Prince Charles allowed to visit his father in hospital when families all around the country are not getting to visit their loved ones who are in hospital when it's not Covid related?" one Twitter user asked.
Even Good Morning Britain host Piers Morgan was vocal in his defence of Charles, writing:
"What an incredibly sad picture. A tearful son after seeing his seriously ill 99yr-old father in hospital. If your first instinct is to spew abuse or rage about Prince Charles visiting Prince Philip today, shut the f*** up."
Charles is the first of the royals to visit Philip in hospital. The heir to the throne is said to have spent around 30 minutes with his father after the 100-mile trip from Highgrove, Gloucestershire to London.
- Additional reporting, NZ Herald