A 70-year-old Swiss-Frenchman claims his father was the illegitimate child of Edward, Prince of Wales - later Edward VIII - and a Parisian seamstress.
Francois Graftieaux writes how a chance remark about his physical resemblance to Edward inspired him to research the connection.
He says the tryst began in 1912, when Edward was staying in Paris with young French aristocrats. The royal in his memoirs mentions visiting the Luna amusement park, which was also a favourite destination of Graftieaux's grandmother, Marie-Leonie.
Marie-Leonie gave birth to a son, Pierre-Edouard Graftieaux, in 1916, but the "father" section on his birth certificate was left blank and she never revealed his identity. However, a platinum and diamond bracelet passed down to Graftieaux's mother when he was born suggests a surprising link to the British royal family.
The bracelet is reportedly identical to one Edward had made for Wallis Simpson, the US divorcee for whom he abdicated in 1936, after less than a year on the throne.
He apparently designed the bejewelled bracelet to feature a "discreetly hidden timepiece so that Wallis Simpson could tell the time at functions without appearing rude to guests", the Daily Telegraph reports.
An affair with the royal would also account for how his seamstress grandmother came into enough money to open her own fashion house in 1916, eventually becoming one of France's most sought-after designers under the name Marcelle Dormoy.
"I believe a secret contract was agreed in which she received money in exchange for her silence on the matter," Graftieaux said. He told the Telegraph he has sent a letter to the Queen to request a DNA test.
"I'm not asking for their love nor their money, nor indeed any power," he added. "I just want to know if my origins, even illegitimate, are to be found here."