Since the introduction of the term public diplomacy (PD), PD literature has evolved and expanded in different directions, multiplying the research conducted on PD actors, programs, publics, networks, tools, and purposes. Focusing our discussion on the purpose of public diplomacy, the potential mission-driven public diplomacy model called “The Golden Circle of Public Diplomacy” by Cabrera Cuadrado (J Public Diplomacy 2:2, 2022) is used to analyze the WHY of Spain’s public diplomacy, analyzing the grand strategy purpose of the European country since the Franco dictatorship until the present day. This analysis comprises the evolution of Spain’s purpose throughout the following phases: the Franco dictatorship, the arrival of democracy (or Transition), and the beginning of the twenty-first century. Interviews to key PD practitioners were conducted to complement the research. An outlook into the future of Spain’s public diplomacy grand strategy is also included.