A new book by Andrew Rose details a little-known affair King Edward VIII had with a French courtesan, and how he was always unfit to be king.

King Edward VIII is best remembered for giving up the throne to marry American divorcee Wallis Simpson. However, Andrew Rose reveals through his new book "The Prince, The Princess, and The Perfect Murder", that this was not the first time one of Edward's affairs had created havoc at the British monarchy.

Twenty years before Edward's abdication, the then Prince of Wales had an affair with French courtesan Maggie Meller, who was later arrested for the murder of her playboy Egyptian prince husband. However, despite the stack of evidence against her, Meller was acquitted in a high-profile trial at London's Old Bailey in 1923. The decision came as a shock to everyone. However, Rose discovered the real reason behind this while doing some research for his book. He found that the acquittal came at the expense of a murder trial, a series of vanished letters and cover-ups to save the grace of the British crown.

According to Rose, Meller used her six years of prior relationship with the Prince to blackmail him into covering up for her and getting her off the hook. "This affair had been carefully airbrushed from history so the connection between the murder and the Prince of Wales was never drawn," Rose told Reuters. "The royal household took steps to make sure that the prince's name did not come out in the trial to protect the reputation of the future king. It is amazing that she got away with it."

The latest book was a follow-on work from Rose's book about the trial, "Scandal at the Savoy", published in 1991. After the release of the book, Meller's grandson contacted Rose, informing him of her affair with the prince, love letters between the two, and a memoir she wrote in 1934.

Meller had struck a deal with the Prince that she would never mention him or their affair if he helped her get off without being convicted.

"Really this was a show trial," said Rose, "The authorities wanted Marguerite to be acquitted. A murder conviction would have been catastrophic for the Crown."

Meller was released and moved back to France where she lived the rest of her life in Paris, dying wealthy in 1971. "This story really does show another side to Edward and how unsuitable he always was to be king," said Rose.