M. Delly or Delly was the pseudonym of the couple of French brothers Jeanne Marie Henriette Petitjean de la Rosiére (Avignon, 1875 - Versailles, 1947) and Frédéric Henri Petitjean de la Rosiére (Vannes, 1870 - Versailles, 1949).Jeanne-Marie and Frédéric were the children of a soldier, Ernest Petitjean, and his wife, Charlotte Gaultier de La Rosière, whose name they took again. They spent their childhood in Vannes before moving to Versailles, after the retirement of their father. In this city, they became friends with their neighbours, the family of Commander Brunot whose wife Marie would become, a few years later, the author of children’s books Marie d'Agon de de la Contrie. Marie, a young dreamer who devoted her entire life to writing, was at the origin of a superabundant work whose publication began in 1903 with Dans les ruines. The contribution of Frédéric is less known in writing than in the skilful management of publishing contracts, several companies sharing this author who was systematically successful. The rate of publication, from several novels a year until 1925, and the very good sales figures ensured the siblings a comfortable income. They did not prevent the two authors from living in perfect discretion, until they remained unknown to the general public and criticism. The identity of Delly was not revealed until Jeanne-Marie’s death on April 1, 1947, two years before that of her brother. They are buried in the cemetery of Notre-Dame de Versailles.Marie and Frédéric Petitjean bequeath part of their fortune and all their manuscripts to the Société des gens de lettres to help the sick or needy writers (Delly scholarship). A room of the Hotel de Massa, seat of the SGDL, is called Delly room.