Edith Piaf has been branded a liar and "an insatiable seducer" in a new biography set to document the truth behind the singer's life.

The book, titled Piaf: A French Myth, which is due to be published in France later this year (13), questions many widely held beliefs about Piaf's personal life and poor upbringing.

Writer Robert Belleret revealed the information after he gained access to unpublished archives which included 110 private letters the singer wrote to a close friend.

He tells The Australian newspaper, "Piaf's duplicity was without limits. She lied profusely about her life, starting with her own birth."

He alleges Piaf, who was famous for her extravagant lifestyle, exaggerated a childhood condition by claiming she was blind between the ages of three and seven, an incident famously documented in the Oscar-winning film, La Vie En Rose.

Belleret adds, "The fact is that she was never blind; at the most she suffered from a viral infection for a few weeks."

The writer also slams Piaf's claim that she smuggled fake French identity papers into Nazi Germany and enabled 200 French prisoners to escape during World War Ii, adding, "My aim isn't to put Piaf on trial, but her account is pure fantasy, it allowed her to avoid punishment after the war.

"She changed the numbers. At first she said she helped 118 prisoners escape, then 147, then more than 200... But not one of them ever surfaced to thank Piaf publicly and to say she deserved a medal. And can you imagine how difficult it would have been to make so many fake identity papers?...

"Every time she meets a new lover she writes that this is the man she's always been dreaming of, but then a month or a year later he's become a rotter... She writes of having two or three lovers at the same time and when she wants to break with a lover she makes him think that he's the one who wants to end it.''

Piaf, also known as The Little Sparrow, died in 1963 aged 47 at her home in Grasse, France, after suffering from liver cancer.