The Duke of Edinburgh, Prince Philip, was admitted to hospital in London on Tuesday evening, according to a statement from Buckingham Palace.
“The Duke’s admission is a precautionary measure, on the advice of His Royal Highness’s Doctor, after feeling unwell,” a palace spokesperson told U.K. media.
The 99-year-old is expected to remain in hospital for observation for a few days.
The duke retired from his royal duties in 2017 and is rarely seen in public. He now spends his days at Windsor Castle with his wife, Queen Elizabeth II.
His illness is not believed to be related to COVID-19. The queen and Philip received a first dose of a vaccine against the coronavirus in early January.
The long-lived duke has had a string of health issues over the last decade.
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.
He was last hospitalized in December 2019. He spent four nights at the King Edward VII Hospital for what the palace said was a planned treatment for a pre-existing condition.
Prince Philip was forced to stop driving at the age of 97 after he crashed his Land Rover into a car in January 2019. He was not injured in the collision, but a woman in the other vehicle suffered a broken wrist.
— with files from The Associated Press