Belle de Jour is said to be the pen name of a former London call girl . Under this name she maintains a successful blog , Belle de Jour : diary of a London call girl which by 2003 had been selected by The Guardian as its blog of the year and has had two books published in both the UK and US Her diary , published as the anonymous blog Belle de Jour : Diary of a London Call Girl became increasingly popular , as speculation surrounded the identity of Belle de Jour , and whether the diary was real .