Never, perhaps, has an heir been more ready for the crown.

Charles, the eldest son of Queen Elizabeth II and a man born to be king, acceded to the throne on Thursday (Friday NZT) after being the designated successor for longer than anyone in the history of the British monarchy. As King Charles III, he will become sovereign of the world's most important constitutional monarchy, head of the most storied royal family and a symbol of continuity in a storm-tossed country.

Having aged from an awkward, self-doubting young man into an unhappy middle-aged husband, Charles has become, at 73, a self-assured, grey-haired eminence, steeped in causes like climate change and environmental protection, which were once quirky but now seem peculiarly in sync with the times.

Whether Charles will ever enjoy the respect or affection showered on his mother is another question. Thrust on to the throne at 25, Elizabeth reigned for longer than most Britons have been alive, anchoring her country with stoic dignity as it made a turbulent passage from globe-spanning empire to reluctant member of the European Union to an uncertain future after Brexit.

Prince Charles in March 1968. Photo / AP

Charles' journey was, perhaps inevitably, less acclaimed. His foibles and frustrations were mercilessly dissected by the news media; his pet hobbies, from architecture criticism to organic farming, were frequently mocked; his marriage to Diana, Princess of Wales, which crumbled amid lurid tabloid headlines and mutual charges of infidelity, remains for many the defining event of his public life.