UK’s Prince Philip, the husband of Queen Elizabeth II, was hospitalised overnight in London as a “precautionary measure”, Buckingham Palace said on Wednesday, reported AFP.

The 99-year-old was taken to the private King Edward VII Hospital on Tuesday evening, Buckingham palace said, adding that it was “a precautionary measure, on the advice of His Royal Highness’s doctor” after the prince felt unwell.

The Duke of Edinburgh, as he is formally known, “is expected to remain in the hospital for a few days of observation and rest”, the palace statement added.

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Sources told AFP that Philip was not taken in by ambulance and had felt well enough to walk into the hospital.

Prime Minister Boris Johnson’s office said he had sent his “best wishes to the Duke of Edinburgh as he undergoes a few days of rest in hospital”.

The prince and the queen, 94, have been maintaining social distancing rules at Windsor Castle because their age puts them at heightened risk from COVID-19 even after receiving their first vaccinations in January.

Prince Philip retired from public duties in 2017 at the age of 96 following a two-night hospitalisation for an infection. He then had a hip operation in 2018.

In January 2019, he emerged unscathed after his vehicle was involved in a traffic accident that injured two people near the monarch’s Sandringham estate in eastern England.

Philip spent four nights at King Edward Hospital in December 2019, where he was treated for what was described as a “pre-existing condition” and was discharged on Christmas Eve that year.