Philip, aged 99, who received a Covid-19 jab in January, was admitted to the private King Edward VII Hospital in London on Tuesday.
The Duke of Edinburgh has been admitted to hospital after feeling unwell, Buckingham Palace said.
He was taken to hospital on the advice of his doctor and a palace statement said it was a “precautionary measure”, with the duke said to be in good spirits.
It is understood the decision to admit him was taken with an “abundance” of caution.
A palace spokesman said: “His Royal Highness The Duke of Edinburgh was admitted to the King Edward VII Hospital in London, on Tuesday evening.
“The Duke’s admission is a precautionary measure, on the advice of His Royal Highness’s Doctor, after feeling unwell.
“The Duke is expected to remain in hospital for a few days of observation and rest.”
Philip has suffered a number of ailments over the years, including being treated for a blocked coronary artery at Papworth Hospital in Cambridgeshire in December 2011 and a bladder infection in June 2012, forcing him to miss the Queen’s Diamond Jubilee celebrations.
Exploratory surgery on his abdomen followed in June 2013 and he began to use hearing aids by 2014, aged 93. He later pulled out of a Battle of Jutland anniversary event in June 2016 citing a minor ailment which was followed soon after by his retirement from public duty in 2017.
He spent four nights at King Edward Hospital in December 2019, where he was treated for a “pre-existing condition” and was later discharged on Christmas Eve.
The duke was then driven to Sandringham and spent Christmas with the Queen.