All subsequent Sultans of the Ottoman Empire kept "Kayser-i Rum" as one of their many titles, including the last one, Mehmed VI, until his deposition on . (Mehmed's cousin Abdulmejid II briefly succeeded him as Caliph and "Amir al-Mu'minin", but never held the Imperial title.) In diplomatic exchanges with the Holy Roman Empire, the Ottomans initially refused to acknowledge the latter’s Imperial claim, because they saw themselves as the only rightful successors of Rome. In the Treaty of Constantinople (1533), the Austrian negotiators agreed not to make any mention of the holy Roman Empire, only referring to Ferdinand I as King of Germany and Charles V as King of Spain. The Ottomans, however, abandoned that requirement in the Treaty of Sitvatorok in 1606, and similarly to the Russian Empire in the Treaty of Küçük Kaynarca in 1774.