Charles Moeller was a Belgian priest and philosopher as well as a specialist in 20th century literature.
He taught philosophy at the Catholic University of Louvain.
During Vatican II he played a major role, particularly in the drafting of Gaudium et Spes.
After the Council, he wrote a book "L'élaboration du Schéma XIII, L'Eglise dans le monde de ce temps" in which he recounted the process of drafting.
In the introduction to this book, he sets out the various stages prior to the Council that contributed to Gaudium et Spes.
Here is the section in which he speaks of Cardijn's role.