British Prime Minister Boris Johnson has expressed his “great sadness” after the royal family announced the death of Queen Elizabeth II’s husband, Prince Philip, at the age of 99. Flags were lowered to half-staff over government buildings after the royals published a statement to confirm the Duke of Edinburgh died “peacefully” at Windsor Castle on Friday morning after his recent hospitalization. Johnson said Philip had “inspired the lives of countless young people,” and “helped to steer the Royal Family and the monarchy so that it remains an institution indisputably vital to the balance and happiness of our national life.” Johnson added that Philip “earned the affection of generations here in the United Kingdom, across the Commonwealth, and around the world.” In its announcement of Philip’s death, the royal family wrote that funeral arrangements will be made “in due course,” and added: “The Royal Family join with people around the world in mourning his loss.”