By the middle of the 20th century religious attitudes had begun to change, but only very slowly. While members of the Roman Catholic Church accounted for approximately 34 percent of the Dutch population, and Catholic political parties had been in coalition governments since 1918, the high fertility rate of the Catholics was a matter of some concern for all non-Catholics.
Fresh memories of Francisco Franco’s association with fascism amplified the crisis over a royal conversion to Catholicism and a marriage without approval of the Dutch States-General. For the second in line to the throne to not only convert to Roman Catholicism, but to also associate with an alleged Franco sympathizer, caused shock and consternation in the Netherlands. When Princess Irene left the Netherlands to join Prince Carlos in Paris after the announcement of their engagement, a threat was telephoned to KLM Royal Dutch Airways by an anonymous caller saying, “you should investigate the plane”.
