http://news.bbc.co.uk/2/hi/uk_news/2644123.stmNewly released FBI files suggest the alleged Nazi connections of Wallis Simpson prevented her marrying King Edward while he was monarch.
The revelations are contrary to the long-held belief that the stumbling block was the American's status as a divorcee.
King Edward abdicated the throne in December 1936, following a constitutional crisis, and married her in exile the following year.
These FBI files were written in the 1940s but are now released under America's Freedom of Information Act.
They suggest stronger connections between the Duchess of Windsor - as she was known after marriage - and the Germans than previously believed.
The documents are a combination of surveillance, informants and hearsay.
One memo said that the British Government, headed by Stanley Baldwin, had known for some time that the Duchess was exceedingly pro-German in her sympathies.
The FBI believed she was considered so obnoxious by the British that they refused to permit Edward to marry her.
Reports emerged last year that the FBI also sent agents to spy on the royal couple after allegations that the Duchess might have been passing secrets to a leading Nazi with whom she was thought to have had an affair.
It is suggested the surveillance had been ordered after President Roosevelt expressed concern about the couple's politics.
/Marcus
