Prince Philip spent a second night at a London hospital after the 99-year-old was admitted for feeling unwell.

Buckingham Palace announced the husband of Britain’s Queen Elizabeth II was admitted to the private King Edward VII Hospital on Tuesday evening. It called the admission "a precautionary measure" taken on the advice of Philip’s doctor.

The Duke of Edinburgh has so far spent two nights in the hospital for an undisclosed reason, the U.K.’s DailyMail reported on Thursday. According to the outlet, he is preparing to spend his third night under the care of medics.

The palace did not immediately respond to Fox News’ request for comment.

PRINCE PHILIP, 99, ADMITTED TO HOSPITAL AS A 'PRECAUTIONARY MEASURE,' PALACE SAYS

Royal biographer Penny Juror told "BBC Breakfast" that chances are the duke isn’t royally pleased by all the newfound attention he’s receiving.

Britain’s 99-year-old Prince Philip has been admitted to a London hospital after feeling unwell, Buckingham Palace said Wednesday. (Reuters)

"I think he can be quite blunt and I think if he felt people were fussing over him he could be quite outspoken about that," said Juror, as quoted by The Mail.

"This is a man who doesn’t want any fuss made on his 100th birthday, so the fact he’s in hospital and getting some fuss made of him will really irritate him."

According to The Mail, palace sources alleged the "sprightly" royal was "in very good humor" before his admission and is in "good spirits" during his stay.

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The palace said Philip is expected to remain for a few days of "observation and rest." His illness is not believed to be related to the coronavirus. The queen, 94, and Philip received the first dose of the vaccine against COVID-19 in early January.

Philip retired from public duties in 2017 and rarely appears in public. His most recent public event was a military ceremony at Buckingham Palace in July.

In this image released on Thursday, Nov. 19, 2020, Britain's Queen Elizabeth II and Prince Philip, Duke of Edinburgh look at a homemade wedding anniversary card, given to them by their great-grandchildren. (Chris Jackson/Pool via AP)

During England’s current coronavirus lockdown, the duke has been staying at Windsor Castle, west of London, with the queen, who has performed duties such as meetings with dignitaries remotely.

Lockdown permitting, the royal household is planning celebrations, to mark Philip’s 100th birthday on June 10.

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Philip married the then-Princess Elizabeth in 1947 and is the longest-serving royal consort in British history. He and the queen have four children, eight grandchildren and nine great-grandchildren.

A former naval officer and keen polo player, Philip enjoyed robust health well into old age but has had a number of health issues in recent years.

In 2011, he was rushed to a hospital by helicopter after suffering chest pains and treated for a blocked coronary artery. In 2017, he spent two nights in the King Edward VII hospital and was hospitalized for 10 days in 2018 for a hip replacement.

Philip retired from public duties in 2017 and rarely appears in public. His most recent public event was a military ceremony at Buckingham Palace in July. (Associated Press)

Philip was last hospitalized in December 2019, spending four nights in the King Edward VII Hospital for what the palace said was planned treatment of a pre-existing condition.

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He was forced to give up driving at the age of 97, after smashing into a car while driving a Land Rover near Sandringham estate in January 2019. Philip needed help to get out of the Land Rover but wasn’t injured. A woman in the other vehicle suffered a broken wrist.

But even after that, Philip continued to drive a horse and carriage on private land from time to time.

The Associated Press contributed to this report.