By Ryan Merrifield King Charles gave a heartbreaking three-word reply the moment he was told his mum had died, according to a new royal book. The new monarch, 75, was out picking mushrooms in the grounds of the Birkhall estate on Royal Deeside, Aberdeenshire, when he was summoned to Balmoral. He got behind the wheel of a Land Rover, alongside Camilla and their team and raced to be at the late Queen’s bedside – although it was too late. Elizabeth’s private secretary Sir Edward Young’s first duty was to tell Charles before anyone else could, writes Robert Hardman in his new biography Charles III…