While it is commonly attributed to Queen Marie Antoinette,there is no record of this phrase ever having been uttered by her. It appears in Jean-Jacques Rousseau’s Confessions, his autobiography (whose first six books were written in 1765, when Marie Antoinette was nine years of age, and published in 1782). The context of Rousseau’s account was his desire for bread, to accompany some wine he had stolen; however, in feeling he was too elegantly dressed to go into an ordinary bakery, he thus recollected the words of a “great princess”.
“Finally I recalled the stopgap solution of a great princess who was told that the peasants had no bread, and who responded: “Let them eat brioche.”
Marie-Antoinette was not only too young but not even in France when it was first published. Rousseau’s Confessions were finished in 1769 and, as Marie Antoinette arrived at Versailles from Austria in 1770, at the age of fourteen, the young Austrian Archduchess, unknown to him at the time of writing his work, could not be the “great princess” mentioned by Rousseau. (x)