Prince Xavier's involvement in 1940 was the Halifax-Chevalier talks. These were secret negotiations between the British and German governments, mediated by Prince Xavier of Bourbon-Parma. The talks were unsuccessful, as Germany demanded the cession of British territories, which Britain was unwilling to accept.
Prince Xavier, Hereditary Duke of Parma Quiz: How Much Do You Really Know About Prince Xavier, Hereditary Duke of Parma?