LONDON — In the world of diplomatic faux pas, it could have been a lot worse. At Tuesday’s state dinner honoring King Charles III and Queen Camilla, U.S. President Donald Trump said that during a private meeting earlier in the day the British monarch had agreed with him that Iran should never be allowed to have nuclear weapons. “We’re doing a little Middle East work right now … and we’re doing very well,” Trump told the audience. “We have militarily defeated that particular opponent, and we’re never going to let that opponent ever — Charles agrees with me, even more than I do — we’re never going to let that opponent have a nuclear weapon.” While many Britons would agree with the president’s sentiment, the comment triggered mild consternation among pundits in the U.K. In Britain, you see, this just isn’t done. By convention, people aren’t supposed to relay private conversations with the monarch.…