"Sleeping with the Enemy: Coco Chanel's Secret Wars" claims Chanel was an agent of Germany's military intelligence organization. It also says Chanel was involved in wartime missions in Berlin and Madrid.
Doubts about Chanel's loyalties during World War II have long festered, but "Sleeping with the Enemy: Coco Chanel's Secret War" goes well beyond those previous allegations, citing as evidence documents culled from archives around the world.
The book, written by a Paris-based American historian Hal Vaughan, was published in the U.S. on Tuesday by Knopf.
The House of Chanel said in a statement that "more than 57 books have been written about Gabrielle Chanel. ?We would encourage you to consult some of the more serious ones."
Vaughan, an 84-year-old World War II veteran and longtime journalist has previously written two other history books and insists that he is serious. He said the book was the fruit of more than four years of intense labor born out of an accidental find in France's national police archive.
Asked why the book, which is chock-a-block with allegations of Chanel's shady dealings before, during and after the war, had turned up so much more dirt than the scores of previous biographies about the fashion icon, Vaughan had two explanations. Firstly, many of the documents he cited had only recently been declassified.
Secondly, he said, many people have a vested interest in protecting Chanel's aura of unsullied chic.
"A lot of people in this world don't want the iconic figure of Gabrielle Coco Chanel, one of France's great cultural idols, destroyed," said Vaughan.
Asked whether he thought "Sleeping with the Enemy" would tarnish the brand's reputation or adversely affect sales, Vaughan snickered.
"There's an expression in French, which translates as 'the dogs bark and the caravans pass,' and that's exactly what's going to happen here with this book," he predicted. Karl Lagerfeld - the brand's current designer whose ponytailed silhouette is almost as iconic as Chanel herself - "is not going to let this thing drift off anywhere, and Chanel will be a name for the next, I don't know, hundred years."
The Associated Press contributed to this report.