Prince Harry is flying to London from California to see his father, King Charles.
The King, 75, has been diagnosed with cancer.
The Prince has spoken by ‘phone to his father and decided to return to the UK straightaway.
His wife Meghan Markle – the Duchess of Sussex – will stay at home with the couple’s two children, Prince Archie, four, and two-year-old Princess Lilibet.
Buckingham Palace has confirmed King Charles will continue with state duties.
These include Privy Council meetings and the completion of Government paperwork in his red boxes.
The King’s diagnosis came after a hospital procedure for a benign prostate enlargement.
The operation revealed a second, more serious medical problem.
The King has started treatment at a London hospital.
However, it has not revealed what type of cancer he has, other than confirming it is not prostate cancer.
Royal biographer Robert Hardman, said:
“We are seeing an upbeat approach from the Royals following the King’s cancer diagnosis.
“I think it’s a case of business as usual as much as it can be business as usual.”
The Prime Minister said his contact with the King will continue “and we’ll crack on with everything”.
Prime Minister Rishi Sunak told BBC Radio 5 Live:
“He [the King] will just be in our thoughts and our prayers.
“Many families around the country listening to this will have been touched by the same thing and they know what it means to everyone.
“So, we’ll just be willing him on and hopefully we get through this as quickly as possible.
“And you know, thankfully, this has been caught early.”
Buckingham Palace statement: