The Duke of Edinburgh was admitted to hospital on the advice of his doctor after feeling unwell.
Prince Philip, who will celebrate his 100th birthday in June, has been admitted as a “precautionary measure”, Buckingham Palace has said.
In a statement, the palace 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."
As Prince Philip, who received a Covid-19 jab in January, 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.
He suffers from arthritis in his right wrist, and broke a bone in his ankle playing polo. He also developed synovitis, a rheumatic condition of the tendon in the hand, after a polo fall.
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 2018 after he was admitted to hospital for treatment relating to a pre-existing condition as the Queen arrived in Norfolk for the royals' Christmas break.
During his Norfolk Christmas stay in January 2019 he also visited hospital for a precautionary check up after his Land Rover ended up on its side in the crash with another car at Babingley on the Sandringham Estate.
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