J.D.'s great-grandfather was Etienne Guillou, surnamed " The Pilot ". He was bom in 1818 and died in 1887.  For all that he was a colourful and worth-knowing person.  He built a wooden house at Concameau on the Quai Pénéroff (today Avenue du Docteur Pierre Nicolas).  The house painted in red and green was in the Bergen style, influence derived from his appointment as vice-consul of Sweden and Norway.

 After his father's death (see § Brittany), J.D. went to live in this house filled up with paintings and travel souvenirs of his family, henceforth belonging to his grand-mother, called Suzanne.  She had just lost her husband, the painter Théophile Deyrolle (see § Heredity) and was running by herself the fish-tank and oyster-bed business started by her father, " The Pilot ".

   At the time, J.D., aged only fourteen, attended the primary school of Concarneau.  Among his numerous cousins, he preferred the company of one of his grand-mother's nieces, Jeannine Guillou, who had the same age.

 Today, the " wooden house " still belongs to J.D's family and the studio on the third floor, where he worked from 1938 to 1942 is still there.