I must confess that this article will be rather short as I have never smelled Le Fruit Defendu, there is almost no information available, and it is unlikely that anyone will be able to sample it (dreams come true though as a full bottle sold at Christies New York a few years back for only $700—it was probably worth ten times that).
Really, the only solid information there is comes from a couple of blogs in French that recount interviews with Jean Kerleo discussing his recreation for the Osmotheque. Mr. Kerleo describes Le Fruit as a flowery woody amber fragrance with strong overtones of almost overripe peach and apricot peel and says that it reminds him of a sweet and salty toffee candy with peach. Bettina Aykroyd, Les Parfums Paul Poiret a l’Osmetheque, Faire le Tour de Monde en Parfums (Jun. 30, 2013), http://faireletourdumondeenparfums.com/les-parfums-paul-poiret-a-losmotheque.
Another source, Olfactorum, recites an interview with Marie Rogeon, the current owner of Parfums Rosine, who reinvented the company as a rose garden in 1991. She tells that Le Fruit was one of the first uses of galbanum and also employed peach, apricot, and almond blossom.
So in summary, it is safe to say that Le Fruit Defende comprises largely of semi-sweet, almost fermented peach and apricot skin (which may give an almost boozy aura) with the green effervescence of galbanum and nutty sweetness of almond blossom over a simple bed of sandalwood, amber, and vanilla.