The Greven Mystery [La Continental : le mystère Greven]

Alfred Greven was the head a French movie studio founded with Nazi money producing propaganda and the most subversive masterpieces of French Cinema. Greven's intentional disappearance after the war and his silence until his death in 1973 maintain a certain mystery. To date, no photos or other record of him are available. Yet the 40 films produced by Continental Films remain. Who was he?