UK’s longest-serving monarch Queen Elizabeth II dies at 96 at Balmoral *ARCHIVE* The UK’s longest-serving monarch, Queen Elizabeth II, passed away on Wednesday at Balmoral Castle in Scotland, at the age of 96. Her doctors confirmed she had been under medical supervision, after becoming concerned for her health. Both of those in the immediate line of succession, her eldest son Prince Charles – now King Charles III- and grandson William, Duke of Cambridge, were with her. Earlier this year, the Queen celebrated her Platinum Jubilee, marking 70 years on the throne. Her husband, Prince Philip, passed away last April at the age of 99. During her reign, 15 prime ministers governed the UK. Her death comes just two days after she invited the latest, Liz Truss, to form an administration, taking over from Boris Johnson.