After many years, book deals and a ITV series, Belle de Jour reveals her identity,

Her name is Dr Brooke Magnanti. Her specialist areas are developmental neurotoxicology and cancer epidemiology. She has a PhD in informatics, epidemiology and forensic science and is now working at the Bristol Initiative for Research of Child Health. She is part of a team researching the effects of exposure to the pesticide chlorpyrifos on foetuses and infants.

http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/books/article6917495.ece