[1] He first became involved in politics with the radical Catholic movements, serving as secretary to Monsignor Louis Picard.
[1] Léon Degrelle had also been a member of Picard's Action Catholique de la Jeunesse Belge and it was that movement's publishing house, Éditions Rex, that inspired the name of Rexism.
[3] Denis two main books were Principes Rexistes and Bases Doctrinales de Rex, both published in 1936.
Within these books he argued that Rex was more of a popular movement than a political party and endorsed a policy that sought to restore dignity to Belgium through a new hierarchical state.
[3] Under the Nazi German occupation Denis collaborated with the occupiers and wrote regularly for Le Pays Réel.