Prince Philip is remaining at the King Edward VII Hospital in London for a second night.
The royal is expected to stay overnight once again on Saturday, one day after Buckingham Palace confirmed his hospitalization on Friday.
“The Duke of Edinburgh travelled from Norfolk this morning to the King Edward VII Hospital in London for observation and treatment in relation to a pre-existing condition. The admission is a precautionary measure, on the advice of His Royal Highness’ Doctor,” the palace said in a previous statement.
On Friday, a royal source told PEOPLE that Prince Philip did not travel by ambulance. “It was a planned admission, and he walked into the hospital unaided,” the source said.
That same day, Queen Elizabeth was seen arriving in Norfolk by train following her annual train ride from London. The monarch traditionally spends Christmas in Norfolk.
It’s unclear how long her husband will stay in the hospital — and if he’ll miss Christmas with the family.
On Saturday, The Telegraph reported that Prince Philip is expected to join his family for the holiday: “Despite increasing fears for the Duke’s health it is hoped he will be discharged and return to Sandringham to join the rest of his family in time for Christmas.”
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Prince Philip retired from his public duties in August 2017. (He has also been absent from Trooping the Colour celebrations since his retirement.)
And in recent years, he has been plagued by health issues.
He abruptly canceled his appearance at the traditional Maundy church service that he was scheduled to attend with the monarch in March 2018. Philip also skipped Easter Sunday services last year ahead of the announcement that he underwent hip replacement surgery.
Last month, Prince Philip and Queen Elizabeth marked their 72nd wedding anniversary but they spent the day apart due to her solo duties in London.