(CNN)Prince Philip has spent a second night in hospital after being admitted earlier this week as a "precautionary measure" following complaints that he was feeling unwell.
Buckingham Palace did not issue an update on the Duke of Edinburgh's health when contacted by CNN on Thursday.
The 99-year-old husband of Queen Elizabeth was admitted to King Edward VII Hospital in London on Tuesday evening, Buckingham Palace said in a press release, issued Wednesday.
According to a royal source, it was not an emergency admission and the Duke traveled to hospital by car and walked in unaided. The source added that the illness was not Covid-19 related.
The Buckingham Palace press release on Wednesday said the Duke's admission was a "precautionary measure" taken on the advice of his doctor after the Prince was "feeling unwell."
"The Duke is expected to remain in hospital for a few days of observation and rest," the press release added.