It is a revelation to the British that the Duke of Windsor once had a love child with a Parisian seamstress. Their grandson claims that the Duke even paid his grandmother to keep quiet and that helped her to rise to become a top fashion designer in Paris.

In a new book, 70-year-old François Graftieaux, grandson of Marie-Léonie Graftieaux, mentions that he has written to Queen Elizabeth II. He asked that a DNA test should be conducted in order to prove his own links with the royalty.

"I'm not asking for their love nor their money, nor indeed any power," he says. "I just want to know if my origins, even illegitimate, are found to be here."

He had been the grandson of a king only in 1936, from January 20 to December 11, 1936. The Duke of Windsor, Edward VIII, had been the king briefly, but abdicated the throne to marry Wallis Simpson.

He had raked up some controversies in the royal family as a womaniser. He had even expressed early admiration for Hitler.

In the book, 'The Man Who Should Have Been King,' the writer says that when the Duke dropped into Paris in 1912, he had an affair with his grandmother, and they had a child. They met in their late teens at a famous amusement park, Luna Park in Paris.

The narrative is said to be clear in the Duke's memoirs as well as his grandmother's diary. 

Just after her son was born in 1916, Marie-Léonie Graftieaux, a seamstress and model for a reputed Parisian designer, just opened a fashion house. She became Marcelle Dormoy and moved on to designing dresses for famous French personalities.

"I believe a secret contract was agreed in which she received money in exchange for her silence on the matter," François told the Telegraph.

However, even though Francois agreed that his grandmother had been "tight-lipped" about the identity of his grandfather, his mother got a Van Cleef & Arpels 'cadenas' diamond bracelet. It had been designed by the Duke of Windsor and works out to be worth £250,000 today (A$430,000).

For a long time, Francois did not think about any connection. It was only after seeing a photograph of the former King that François felt it was the "spitting image" of his father.