Prince Charles says he’ll temper his opinions if he becomes king

LONDON — Prince Charles has not been afraid to speak his mind on topics like historical preservation, climate change and alternative medicine. But as king, should that come to pass, it would be a very different matter, he acknowledged.

“I do realize that it is a separate exercise being sovereign,” the prince said about his activism in a documentary, expected to air on the BBC Thursday night, on the occasion of his 70th birthday next week.

“The idea, somehow, that I’m going to go on in exactly the same way, if I have to succeed, is complete nonsense because the two situations are completely different,” he said, referring to the roles of heir and king.

The interview offers a rare glimpse of what Charles might be like as king, and is perhaps an effort to assuage critics who have worried that he would diverge from British monarchs, who are bound by tradition to reign, not rule, over their subjects.

His mother, Queen Elizabeth, now 92, was crowned in 1953, and is the longest-serving British monarch, having surpassed Queen Victoria in 2015. She is queen of 15 other nations, including Canada.

Though many in the British public — and around the world — follow the lives of the Royal Family closely, any strong personal views that the Queen might hold have largely remained private in her nearly seven decades as sovereign. Her opinions on matters of government and other issues have been concealed behind a polite smile and signature wave.

As king, Charles may face another hurdle: his popularity lags behind the queen’s and that of his sons, William and Harry.