duumvirate

noun2

1. •
   (historical) Any of several offices of the Roman Republic held by two joint magistrates known as duumvirs.
2. •
   Synonym of diarchy: rule by two people, especially two men.

   • To replace the all-powerful Salan, de Gaulle appointed a duumvirate – Paul Delouvrier and General Maurice Challe. — 1977