A band of brothers? Capetian princes in Anglo–French diplomacy, 1230s–1260s.

This article examines the political and diplomatic roles of Robert of Artois, Alphonse of Poitiers, and Charles of Anjou, the brothers of King Louis IX of France (1214–70), highlighting their unique position within the Capetian monarchy. Unlike the Plantagenet dynasty, where royal brothers played prominent and often contentious roles, Louis IX's brothers held apanages—territorial grants that reinforced royal authority without threatening the indivisibility of the kingdom—and operated largely in the king's shadow, with their diplomatic involvement closely tied to his presence and policies. The article contrasts their relatively subdued participation in Anglo-French diplomacy with the more active and documented roles of Henry III of England's brothers, Richard of Cornwall and Simon de Montfort, who despite familial conflicts, were central to English diplomatic efforts. The Treaty of Paris (1259) further illustrates this divergence, as Louis IX's brothers were largely absent from negotiations and formal renunciations, underscoring the evolving nature of Capetian royal power as increasingly centralized and individualized under Louis IX.