In 1809, a Spanish ship carrying Fernando VI’s ambassador, Juan Jabat y Aztal, arrived in the Straits of Gallipoli, beginning years of negotiations in the Ottoman capital over his legitimacy. Fernando VII had already abdicated “voluntarily” and was being held by the French in Bayonne, although he was still recognized as King of Spain by the Council of Castile and by England. The Ottomans had to make a choice. Juan Jabat was allowed to pass from the Straits to Constantinople because “there was no hatred and enmity between the Sublime Porte and the nation (millet) of Spain, and it was not known whether the people on the ship were from the nation (millet) and the republic (cumhur).” However, he was not allowed to stay in the Spanish embassy as the Ottomans did not accept the legitimacy of the abdicated king. This paper examines debates between Ottoman officials, the British and French ambassadors, and Juan Jabat between 1809 and 1814 to argue that the tactical use of concepts such as state (devlet), nation (millet), and republic (cumhur) made and unmade diplomacy. Debates over the legitimacy of the ambassador among representatives of four different powers show how diplomacy had become a network of different states debating issues in a plurilateral fashion. The arguments of the parties involved demonstrate how hierarchies were created and negotiated through arguments of legitimacy that depended on the key concepts of the Age of Revolutions. Diplomacy, in this sense, is already at work before the ambassador is officially received, before a proper ceremony can be held for him and before he can focus on the daily tasks of his post. Using diplomatic documents from the Presidency Ottoman Archives in Istanbul, I employ the tools of conceptual historians to examine how concepts are used politically in diplomatic encounters to create or deny legitimacy, and how the different meanings given to concepts shape diplomacy as a field of negotiation in the specific case of Juan Jabat y Aztal’s embassy.