The Duke of Edinburgh has spent a fourth day in hospital in London being treated for a "pre-existing condition".
The Queen is at the Sandringham Estate in Norfolk, where she attended a carol service without 98-year-old Prince Philip on Sunday.
He remains at the King Edward VII's Hospital in central London, having travelled there on Friday as a "precautionary measure".
The Prince of Wales said his father was "being looked after very well".
Speaking on a visit to Fishlake, South Yorkshire, Prince Charles added: "At the moment that's all we know."
Buckingham Palace said the admission was for "observation and treatment".
The duke went to hospital on the advice of his doctor, it said in a statement.
It refused to confirm or deny reports the duke was flown to London by helicopter and then driven by car for the last part of the journey.
The duke, who retired from official solo royal duties in 2017, walked into hospital and was expected to remain there for a few days.
The Queen did not change her schedule and left Buckingham Palace for Norfolk by train, to begin her traditional festive break at Sandringham, where the duke has spent much of his time since stepping back from public duties.
She is expected to return to St Mary Magdalene Church on Christmas Day, having attended on Sunday with Prince Edward and his family.
The monarch was pictured stepping out of a car before walking into church ahead of her grandchildren, Lady Louise Windsor and Viscount Severn.