I’m not usually tempted by biographies of royals, living or not long dead. They tend to be written in deferential tones and I prefer something neutral or, better yet, something with teeth. However, twenty years ago, when I was preparing to write my novel Gone with the Windsors, I read a huge number of books about the Duke and Duchess. Panegyrics, hatchet jobs, you name it. Hugo Vickers’s Behind Closed Doors had yet to be published. When it came out in 2011, I felt compelled to read it. Vickers had no axe to grind. He hadn’t known the Windsors. Could he deliver the sharp-eyed skinny?