An infamous photo showing Margaret, Duchess of Argyll performing a sex act on a man shocked the nation when it was produced as evidence in her divorce proceedings.
But the man’s head was cut off in the photo, leading to feverish speculation as to who he was.
Suggested candidates have included Winston Churchill’s son-in-law Duncan Sandys, then the defence minister.
But Margaret’s daughter-in-law, Lady Colin Campbell, told a Sunday newspaper the man was William “Bill” Lyons, sales director of Pan American World Airways and Margaret’s lover.
The 1963 divorce case humiliated the Duchess but enthralled the public with its salacious detail, including claims by the Duke of Argyll that his wife was unfaithful with 88 men.
Lady Campbell said the time had come after 50 years to reveal Bill as “the headless man” because by keeping the mystery going “we have done Margaret’s reputation no favours”.
She said that Margaret had begun seeing Bill, himself a married man, after the Duke began divorce proceedings against her.
Lady Campbell added: “To those of us who were close to her it was hardly a surprise. Bill was her lover, after all.”