Theo Van Doesburg Marries Petronella Johanna van Moorsel

In 1920 Nelly met Van Doesburg through her brother, who had a subscription to the magazine published by Van Doesburg De Stijl.

At the opening of the exhibition La Section d'Or in The Hague on July 11, 1920 she became instantly in love with him. Her Catholic parents argued, however, no price on the deal with Van Doesburg, who was not only Protestant but married. Therefore, she walked around the turn of 1920-1921 away from home. They were caught in Leiden by JJP Oud and his wife Lena Milius. During her relationship with Van Doesburg, she was introduced to the world of modern art. For instance in March 1921, Van Doesburg took her on a lecture tour in Europe, where they were visiting Piet Mondrian in Paris.

From April 1921 she lived with Van Doesburg in Weimar . In December, she spent several weeks in Vienna, to reflect on its future. Here she met the Hungarian artist Lajos Kassak , publisher of the journal Ma. Aktivista Folyóirat (Activists Today Magazine). This created a correspondence between Kassak and Theo van Doesburg.