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The Duke of Edinburgh, Queen Elizabeth II’s husband, was admitted to the King Edward VII 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,” according to the statement.

Prince Philip, 99-year-old, is expected to remain in hospital for a few days of “observation and rest,” the palace said.