AD SERENISSIMUM REGIÆ STIRPIS PRIMUM PRINCIPEM LUDOVICUM BORBONIUM CONDÆUM BURDEGALÆ ET AQUITANIÆ PROREGEM OPTATISSIMUM.
As one can see, this "Ludovicum Borbonium," whom I believe to be Louis II de Bourbon, is is referred to by the Latin title Proregem (or Prorex in the nominative case). What exactly does this Latin title mean in reference to Louis II of Bourbon? What would have been the French equivalent? What was his royal position?