Long before the abdication crisis broke in 1936, detectives were trailing Mrs Simpson through London high society in an attempt to discover more about the American woman who had captured the Prince of Wales's affections.
The revelation is buried in 100 files about the abdication of Edward VIII and the government's subsequent relations with him. The papers are released today following the death last year of the saga's last big player, the Queen Mother.
Although the papers will not radically alter historical accounts of the abdication they certainly add colour and background detail.
They do not substantiate long-held rumours that the government compiled the so-called China dossier on Mrs Simpson's sex life in the 1920s, or that she and the duke were substantial Nazi sympathisers. Nor do they confirm that the Queen Mother was instrumental in forcing the couple out of the country.
Deep inside a Metropolitan police file are several reports, stamped "secret", that record officers' pursuit of vicious gossip about the already twice-married Mrs Simpson.
One of the first police reports, dated June 25 1935, opens on a note of frustration. "The identity of Mrs Simpson's secret lover has not yet been ascertained.
"Mrs Simpson is very jealous of a woman whom POW [the Prince of Wales] met on his recent visit to Austria. This woman has since been to London and spent time with POW.
"Mrs Simpson is, in consequence, apprehensive of losing the affection of POW which she is very anxious to avoid for financial reasons. She is therefore extremely careful and is spending as much time as possible with POW and keeping her secret lover in the background."
By that time Mrs Simpson was already a frequent visitor to Fort Belvedere, Prince Edward's private residence near Windsor. The report notes that her then husband, Ernest Aldrich Simpson, the heir to an Anglo-American shipping fortune, was well aware of her affair with the prince and hoped to profit from it. "[Mr Simpson] has mentioned that he expects to be created a baron. He is very talkative in drink."
Another police report, undated, mentions Mrs Simpson's closeness to Prince Edward. "Mrs Wallis Simpson visited an antique shop in Pelham Street, South Kensington, in company with POW. The conversation showed they were on very affectionate terms and addressed each other as darling.
"The opinion of the dealer expressed after his distinguished client had left was that the lady seems to have POW completely under her thumb."
A later report, dated early July 1935, opens with a triumphant revelation. "The identity of Mrs Simpson's secret lover has now been definitely ascertained. He is Guy Marcus Trundle, now living at 19 Bruton Street [in Mayfair]."
The 36-year-old Trundle, the report said, was a charming adventurer, good looking, "well bred" and an excellent dancer.
"Trundle is a motor engineer and a salesman and is said to be employed by the Ford Motor Company. It is not known what salary he gets ... Trundle claims to have met POW through Mrs Simpson.
"He is said to boast that every woman falls for him. He meets Mrs Simpson openly at informal social gatherings as a personal friend, but secret meetings are made when intimate relations take place."
