The Daily Express reports, "Wallis Simpson wasn't the first mistress to threaten Edward VIII's reputation." (Thank you to Dawn for this link!)
The book The Woman Before Wallis by Andrew Rose, about Marguerite Alibert's love affair with the future Edward VIII, is available from Amazon.com.
From the Daily Express: "Royal playboy Edward VIII's reckless weakness for risky affairs has been laid bare in an extraordinary expletive-ridden letter to a mistress."
November 25 UPDATE:
King Edward VIII's foul-mouthed love letter fetches a princely £5,100 at auction