This week sees the publication of Traitor King, the fascinating new book by bestselling history writer Andrew Lownie.

Lownie’s previous books have focused on the lives of Guy Burgess and the Mountbattens.

This time he has chosen the Duke and Duchess of Windsor as his subject.

Traitor King offers a remarkably detailed and refreshingly different outlook on their lives.

While most biographies of the couple finish with the 1936 abdication, this is the point where Lownie’s investigation begins. His focus is on what happened next and the decades of exile that Edward and Wallis’ love match forced them into (although never mentioned, the modern-day parallels with the Duke and Duchess of Sussex are difficult to ignore).

When I caught up with the author earlier in the month, he explained how the Windsors’ relationship bent and buckled under the strain.

Far from the ‘happily ever after’ image they tried to depict, the pressure of living as one of the most famous romances of the century created huge tensions.

The book also discusses the role the couple played in the run up to

and during the Second World War, over relations with Nazi Germany.

The traditional take is that the Duke was no different to much of the aristocracy at the time, reaching out to try and avoid the horrors of another World War One: in doing so, the Duke ended up as an unwitting pawn in Nazi plans for him to be a British Pétain in the event of a German invasion. Lownie argues that far from being foolish and naïve, the Duke was in fact well aware of what the Germans wanted. In summer 1940, when the Duke and Duchess had fled France

for Spain, they had numerous communications with the Germans via Spanish emissaries, which were not reported back to the British.

The ‘killer telegram’ for Lownie came on August 15 1940, when the couple agreed to stay in touch with the Germans using a special code, should the situation change.

Lownie’s research for the book has been fastidious.

Some of the material has been readily available, but as Lownie describes it, left alone by other historians.

Other sources remain harder to come by.

Researching his previous book on the Mountbattens, Lownie famously found himself blocked by the Cabinet Office and Southampton University, despite buying their archive to ‘ensure public access’ in 2011.

It’s an engrained culture of secrecy that will continue unless challenged: Lownie describes Prince Charles as being ‘cut from the same cloth’ as the Queen in his belief of protecting the family’s reputation and not letting ‘the daylight in’.

Lownie, by contrast, sees it as the historian’s duty to help pull the curtains back.