Anyone who was at Eton in the mid-'90s, when Prince William was a student at the élite English boarding school, would hardly have noticed there was a royal in their midst. There was the solitary uniformed policeman standing outside the boys' house where he lived (his plainclothes bodyguards were harder to spot). And there was the fact that, while teachers referred to most students by their last names, he was just William. Otherwise, he was treated like any other student — except on the rugby field. When the prince joined one of the school's junior rugby teams, "it suddenly...