Bombs start exploding at the beginning of this book. Buckingham Palace was targeted by the Nazis early on in the war in an act of extraordinary audacity – and one that backfired. George VI noted in his diary: ‘We all wondered why we weren’t dead.’ Little did he realise that Hitler had gifted him his first wartime ace. But while George grew into the role of stoic monarch, his older brother never worked out how shake off the trammels of his birth.

The Windsors at War is a follow-up to Alexander Larman’s The Crown in Crisis, which explored the abdication of 1936. Edward VIII did not escape lightly in that book, and this sequel’s introduction reminds readers of the author’s earlier crushing conclusion: that the failed king was a ‘wretched, quixotic ruler, an obsessed and demanding lover, and, bar the odd instance of compassion and decency, a selfish and thoughtless man’. Needless to say, post-abdication, things don’t start well for the exiled duke, whose outsized ego and solipsistic tendencies were a national liability amid mounting geopolitical tension.

We relive Edward’s fateful visit to Nazi Germany in 1937, and the subsequent American snub when his transatlantic trip was cancelled. There are frosty communications between the duke, the insecure king and various lackies, in what amounted to a half-baked effort to cancel the former monarch. (The charismatic Edward would rarely be allowed back to his country again.) And we return to the duke’s exit from France, via Spain and Portugal, in the summer of 1940 – the ‘will-he-defect-to-the-Germans?’ moment before the couple were ignominiously bundled off to the Bahamas.

Aspects of The Windsors at War, of course, have a painful resonance. Just as Hilary Mantel mused that Edward’s great-great-nephew the Duke of Sussex ‘doesn’t know which he is, a person or a prince’, the same could be said of the defunct monarch. The duke rejected kingship for married life; but did he know how to be a person? Shadow-boxing his legacy made Edward a potentially dangerous man. We hear much about the characters in the British orbit who rallied to contain him, and of the Axis’s efforts to entrap him. That Edward was ultimately loyal only to himself and his wife gave the couple a wild-card quality.

Larman dissects the messages, letters and general communications from all sides in an attempt to ascertain the extent of the duke’s foul play. It is a report by the Spanish diplomat Don Miguel Primo de Rivera that proves most revealing. Rivera concluded that the couple were ‘completely enmeshed in conventional ways of thinking’. They had assured him that any idea of returning them to Britain and the throne was out of the question, courtesy of the British constitution. It seems not to have occurred to the duke that a fascist Britain might play by different rules.

Edward would always be the product of the monarchical system he’d been raised in. He couldn’t escape institutional thinking, even when enticed by the enemy and snubbed by the British (governor of the Bahamas, indeed!). Again, there are modern parallels. Edward was hurt, angry and rudderless, which resulted, if not in treason, certainly in disloyalty. The Duke of Sussex is also angry, hurt and seemingly rudderless while still insisting he’s a monarchist, with unedifying results for the royal family and Britain.

The Windsors at War centres on what happened after Edward gave up the throne for the woman he loved. It is a keen reminder that making a fist of life outside the royal cage was far harder than the former king had reckoned on, with painful ramifications not only for himself but for his brother trapped inside. It is a detailed and fascinating account; but it is men’s history, written by a man, and the female players are largely missing. Though Wallis, according to Larman, was the driver behind much of Edward’s thinking, this American, whose style and acerbic appeal were acknowledged and abhorred in equal parts, remains a shadowy figure. Where was her head during the war, and who was really in control? Ditto the ‘clever’ Queen Elizabeth, who never forgave her sister-in-law. Surely both had more depths to explore than the weak men they served to prop up.

In the end – as history dictates – the winner of the book is the tired George VI (incidentally, an appeaser before the war), who, standing beside his new friend Winston Churchill on VE Day, waved from the palace balcony to the hordes below. Larman remains unsympathetic to the man whom the monarchy discarded with a post-war shrug: ‘Edward was told that any job under the crown was now impossible.’ He concludes that it required the accession of Elizabeth II to ‘neutralise the threat’ the duke posed. Perhaps. But after her 70-year reign, the House of Windsor appears not to have learned very much about handling sensitive royal players who don’t fit inside the box.