“I’m not that stupid,” said Charles, Queen Elizabeth II’s eldest son, when asked whether he would continue to publicly campaign after he becomes king. “I do realize that it is a separate exercise being sovereign. So of course I understand entirely how that should operate."

The comments, which come from a one-hour BBC documentary, “Prince, Son And Heir: Charles At 70,” mark the first time he has publicly addressed concerns that he could be a meddling monarch.

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Unlike his inscrutable mother Elizabeth, who can discuss issues like Brexit in neutral tones, Charles has triggered criticism — and praise — for his controversial views. Perhaps most famously, he once called a planned extension at London’s National Gallery a “monstrous carbuncle.” (The design was later scrapped.)

The expected future king also came under scrutiny after the publication of a cache of letters he penned to government ministers — dubbed the “black spider memos” because of Charles’s scrawled handwriting — that showed him to be a supporter of a number of causes.

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“Charles will never be neutral just as he will never be party political,” wrote Catherine Mayer in her book “Charles: The Heart of a King.” She continued: “For better or for worse — in my final analysis, more often for better than for worse — the Prince is a man with a mission, a knight on a quest.”

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Charles, who turns 70 next week, is the longest-serving heir apparent in British history. In the BBC documentary, he said that he will operate within “constitutional parameters” when he becomes monarch, which is a “completely different” role from being the Prince of Wales, as the heir in Britain is known.

“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 — the two situations — are completely different,” he said, according to excerpts from the documentary released ahead of its broadcast Thursday evening.

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The documentary features interviews with his sons Prince William, who said he would like to see his father spend more time with his grandkids, and Prince Harry, who praised his father for walking Meghan down the aisle when her own father couldn’t make the wedding.

While Charles said he understood that being king would be different from being heir, he did defend his activism.