The third man: Mr Trundle the car dealer

Wallis Simpson kept a "very charming" car salesman with a talent for dancing as a secret lover while she was married and being courted by the future King Edward VIII.

The relationship with Guy Trundle, a Ford dealer from Mayfair, was discovered in 1935 by Special Branch. Detectives had been ordered to keep Mrs Simpson and Edward, then Prince of Wales, under close surveillance and send regular reports on their relationship to Scotland Yard.

The revelations are contained in previously unseen Public Record Office files.

Initially, the officers had difficulty establishing the identity of her paramour, noting only that Mrs Simpson was being "extremely careful" to conceal his existence from both Edward and her husband, Ernest. But in a report dated 3 July 1935, the detectives said they had tracked down Mr Trundle, a 36-year-old "motor engineer and salesman" who was married to the daughter of a Royal Tank Corps general.

The report continued: "He is described as a very charming adventurer, very good looking, well bred and an excellent dancer. He is said to boast that every woman falls for him."

Special Branch said it was confident that the relationship was sexual. "He meets Mrs Simpson quite openly at informal social gatherings as a personal friend but secret meetings are made by appointment when intimate relations take place," it said.

Mr Trundle, who was four years younger than his lover, received regular payments from Mrs Simpson as well as expensive presents.

An earlier report by Special Branch describes Ernest Simpson as, "a bounder type who makes no secret of his wife's association with the POW" (Prince of Wales).