Prince Harry reportedly called The Queen last week to ask for updates on the health of his grandfather Prince Philip.
The Duke of Edinburgh, 99, was admitted to the private King Edward VII hospital in North London on Tuesday night for a mystery illness that is not coronavirus-related.
Doctors initially expected him to be kept in for observation for a few days but he is now about to spend his sixth night at the hospital - and fears over the seriousness of his condition were raised on Saturday when Prince Charles made a 200-mile round trip to visit him.
Harry, who is currently living in California with his wife Meghan Markle, announced last week that the couple would not be returning as working members of the Royal Family, just before Philip was taken to hospital.
According to the Daily Mail, the Duke of Sussex called his grandmother following the news and is prepared to travel to the UK if his condition worsens.
Harry is said to be isolating with Meghan and their son Archie and has a private plane on standby to bring him to the UK if required.
Buckingham Palace has given no further updates on Philip's health over the last few days.