In 1883, Wytsman was a founding member of "Les XX", the famous avant-garde group in Brussels, inspired by the figure of Octave Maus, and founded by Frantz Charlet, Jean Delvin, Darío de Regoyos, Paul Du Bois, James Ensor, Willy Finch, Charles Goethals, Fernand Khnopff, Pericles Pantazis, Frans Simons, and Théodore Verstraete.