Spirou the Diplomat (Spirou Diplomate in the original French) is a comic one-pager possibly written by Rob-Vel, and drawn by either him or Luc Lafnet. It features Spirou, Adolphe Max and Adolphe Max's Dog.
Behind the scenes
This one-pager was released in June of 1938 in Le Journal de Spirou #12 in Belgium. It was reprinted in the Spirou par Rob-Vel collection of all of Rob-Vel's Spirou comics. It has not known an official English printing to this day.
Adolphe Max was indeed mayor of Brussels in 1938.