Hugo was educated at a boarding school led by nuns in Aalbeke and experienced the German occupation of Belgium during World War II. The experience was formative, and would later be adapted by Claus into his semi-autobiographical "The Sorrow of Belgium" (1983). Many of Claus' teachers were Flemish nationalists who were sympathetic to fascism, and Claus joined the pro-German youth wing of the Flemish National Union. His father was also briefly detained after the Liberation for collaborationism. A sympathizer of the political left at a more mature period in his life, Claus lauded the socialist model after a visit to Cuba in the 1960s.