
Prince Philip, 98, travelled from the Sandringham Estate in Norfolk to London's King Edward VII Hospital on Friday as a "precautionary measure".
Another source, who also said the Queen and Philip have been living apart for months as the Duke made a decision to leave Balmoral in early September to stay in Sandringham, added the senior royal suffered "a bit of a wobble" this autumn.
The Queen attended church in Norfolk on Sunday, after the Duke of Edinburgh spent his second night in hospital.
Buckingham Palace released a special holiday photo showing the queen making Christmas desserts with her son, Prince Charles, her grandson Prince William and her great-grandson Prince George.
That said, the Queen reportedly spoke to the Duke prior to him being transferred to King Edward VII Hospital in London and is being kept informed of his condition.
While the palace has downplayed the Duke's admission as "pre-planned", a royal expert claimed the Queen's reaction suggests that it's business as usual for the monarch herself. He has also been admitted to hospital with various complaints over the past decade.
While Prince Philip remains in hospital, the surrounding streets are full of TV satellite trucks from around the world, waiting to broadcast the latest news on his condition.
"The admission is a precautionary measure, on the advice of his Royal Highness' doctor".
A royal source previously told PEOPLE that Prince Philip did not travel by ambulance.
She caught the 10:42 GMT Great Northern service from London's King's Cross and was later pictured stepping off the train at King's Lynn railway station.
However, the Daily Mail reported yesterday Prince Philip was transported from Wood Farm, the five-bedroom cottage he has been staying since early September, to London in a helicopter, fuelling concerns over his health.
According to a source, this Christmas could mark the debut in the walkabout to the chapel of both Prince George and Princess Charlotte.
Since 1952, The Duke of Edinburgh carried out thousands of appearances alongside Her Majesty.
His decision to retire from public duties during 2017 was not health-related, Buckingham Palace said at the time of the announcement.