Netflix’s The Crown has revolutionised the way we view the royal family, triangulating as it does between three competing sources: the truth, fiction and rumour. When we mourned the Queen last year, many of us, I think, will have intermixed memories of her from real life with the far more intimate and revealing portraits we got from The Crown. The royal family and their various hangers-on are burnished in the series by their place in a stream of narrative, the jagged edges of real life smoothed; they are summoned into life by a kind of communal act of magical thinking.

All of this, of course, presents a challenge for the royal biographer. We come to this family and their story with expectations of drama and revelation, entertainment and scandal. And yet it is a family that seeks – with a few notable exceptions – to maintain an air of haughty secretiveness, revealing as little as possible of its inner workings.

Alexander Larman is a firmly post-Crown biographer. He recognises the frisson that we all require from our encounters with royalty now, delivering them with knowing winks and fruity nods. The Windsors at War is the follow-up to his much-praised The Crown in Crisis, continuing the story of the absurd and rakish Edward VIII now he is merely Edward, Duke of Windsor, “former king and continued irritant”. This book is even more rollicking than its predecessor – this is an author having an enormous amount of fun with his subject. Whereas in The Crown in Crisis, Larman had described Edward as “a wretched, quixotic ruler, an obsessed and demanding lover and, bar the odd instance of compassion and decency, a selfish and thoughtless man”, here he doubles down: “My only regret is that I have been too generous towards him.”

The Windsors at War opens with a passage told with great imaginative brio from the perspective of a German pilot flying low down the Mall to bomb Buckingham Palace in 1940. It was the first week of the blitz and King George and Queen Elizabeth were only saved by the fact that they had left the windows open. Six bombs were dropped in all, with few injuries. Here we first get a sense of Queen Elizabeth’s personality: charming yet austere, Victorian in her propriety and yet warm-hearted. “I was so pleased with the behaviour of our servants,” she wrote to her mother-in-law, Queen Mary, “they were really magnificent.” Later, she said, famously: “I’m glad we’ve been bombed. It makes me feel I can look the East End in the face.”

There is more to this book than mere titillation. What Larman does so brilliantly is to give us two brothers who could not be less alike, two wives who clearly loathe one another, visions of two very different, but very loving marriages. He draws on a host of previously unpublished material, much of which concerns Edward and Wallis’s Nazi sympathies. Goebbels affectionately called the duke “a tender seedling of reason”, while the duke and Göring play with a toy aeroplane that dropped wooden bombs on to a convoy of trains below.

Much more interesting than this is the strange and febrile dynamic of the relationship between the two brothers: the money-hungry, vain and infantile Edward and the king, whom Chips Channon called “the dullest, most boring but well-meaning little man on Earth”. As the country is drawn into war, King George exhibits reserves of courage and self-restraint whose impressiveness is only highlighted by the peevishness of his foppish brother, flouncing around the Bahamas as a “wandering minstrel”, worrying about his and Wallis’s titles, their reserves of cash.

You wonder about the future of The Crown (as one wonders, perhaps, about the future of the crown). It is fast closing in on the present day, its hyperreal narrative speed catching up with the more stately march of real events. Perhaps, once the two collide, Netflix could step back in time – certainly The Windsors at War feels like it would make for a riotous and thoroughly engaging piece of television.

• The Windsors at War: The Nazi Threat to the Crown by Alexander Larman is published by Weidenfeld & Nicolson (£25). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply