The Duke of Edinburgh was in hospital on Wednesday night after being admitted following a short period of illness.
The Duke, who turns 100 in June, was admitted to the King Edward VII Hospital in London on Tuesday evening and is said to be “in good spirits”.
His admission was “a precautionary measure” on the advice of a palace doctor.
The Duke was taken to hospital by car and walked in unaided. It was not an emergency admission. A palace source confirmed it was not Covid-related and said the stay in hospital was “purely precautionary”.
The source said the Duke had been “feeling unwell for a short period and the doctor was called”.
An insider added: “The phrase that was used by his doctors was ‘an abundance of caution’. Obviously, you can never be too careful when patients are the Duke’s age.”
The Queen remains at Windsor Castle, where the couple have been self-isolating for the majority of the past 12 months.
Boris Johnson led the nation in sending his best wishes to the Duke for a speedy recovery.
A Number 10 spokesman said: “The Prime Minister sends his best wishes to the Duke of Edinburgh as he undergoes a few days of rest in hospital.”
Prince Charles and the Duchess of Cornwall continued to carry out their first royal duties of the year, meeting volunteers taking part in clinical vaccine trials in Birmingham on Wednesday.
Having been hunkered down together in “HMS Bubble” with a small retenue of staff, the Queen and the Duke received their coronavirus vaccinations on January 9 from a household doctor at Windsor Castle.
The Duke’s health concerns over the years
Prince 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 that forced him to miss the Queen’s Diamond Jubilee celebrations.
The last time he was in hospital was in December 2019, when he spent four nights at King Edward Hospital to be treated for a “pre-existing condition”. He was discharged on Christmas Eve before being driven to Sandringham to spend Christmas with the Queen.
Before that, he spent 10 days in hospital following a scheduled hip replacement.
In June 2016, he pulled out of a Battle of Jutland anniversary event, citing a minor ailment, which was followed soon afterwards by his retirement from public duty in 2017.
In June 2017 the Duke was admitted to hospital after becoming ill with an infection arising from a pre-existing condition. He spent two nights at the King Edward VII hospital as a precautionary measure on the advice of a doctor, meaning he missed the State Opening of Parliament and Royal Ascot.
Prince Charles accompanied the Queen instead of his father to the State Opening of Parliament – the 11th time he had missed the occasion since 1956.
The Duke underwent exploratory surgery on his abdomen in June 2013, and he began to use hearing aids by 2014, when he was 93.