On a special episode of Palace Confidential, host Luke Blackall sits down with esteemed royal author Hugo Vickers to discuss his 2011 book on Wallis Simpson, which has inspired a new feature film.

As author of Behind Closed Doors: The Tragic, Untold Story of the Duchess of Windsor, Vickers was brought in as historical consultant on the film My Duchess, starring Dame Joan Collins, Isabella Rossellini and Charles Dance. The film has no set release date.

The movie follows the lonely final years of Wallis, still in effective exile in France, between the death of her husband, the former King Edward VIII, in 1972 and her own in 1986.

During the wide-ranging interview, Vickers drew a historical parallel between Edward and Prince Harry, who he claims have both been left looking miserable after turning their backs on the royal family.

Edward infamously abdicated on 11 December 1936, after the Government refused to accept his marriage to American socialite and divorcee Wallis Simpson.

The royal author said: 'I sometimes show in lectures a picture of the Duke of Windsor with really dead, sad eyes, aged 70.

'I saw him once at Princess Marina's funeral. I have never seen a man with such sad eyes, deep into his soul.

'Then, I show a picture of the Queen with sparkling eyes, aged 88, opening Parliament. The one who did her duty and the other who took the path of perceived happiness.

'If ever you have to choose between the two, duty will always make you happier in the long run. You see that with Prince Harry, he took a different path and he looks utterly miserable.'

Elsewhere in the show, Vickers rejected comparisons between Wallis and Meghan Markle.

'The only comparison between Meghan Markle and the Duchess of Windsor is that they're both American and both had previous husbands. Otherwise, it ends there,' he said.

'Because, actually, the Duchess of Windsor looked after the Duke extremely well. He ate really delicious food in beautiful surroundings.

'She was very stylish and elegant and what she was doing, in a sense, which is so interesting, is keeping the myth alive that this was the greatest love story of the 20th century.

'He had put her in a very difficult situation. He turned her into the world's most hated woman in certain circles.'

Hugo Vickers' Behind Closed Doors, the gripping true story behind the new film My Duchess, is available now.

Watch the full episode, where Vickers revisits the Duke of Windsor's controversial links to the Nazis, by subscribing to Palace Confidential on YouTube.