History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously divided the administration of the eastern and western portions of the Empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
List of Roman and Byzantine Empresses
The Western Roman Empire met its end in 476 and the Eastern Roman Empire in 1453. Although others continued to claim similar titles after the Fall of Constantinople in 1453 — e.g. Holy Roman Empresses (as heirs of the Western Empire) or Russian Tsaritsas and Empresses (as the Empresses of the Third Rome) — the last reigning Empress consort of the Eastern Roman Empire of Constantinople was Maria of Trebizond. The last Palaiologan pretender, Andreas Palaiologos, sold his right to the imperial succession to Charles VIII of France, but he also willed the imperial titles to Ferdinand II of Aragon and Isabella I of Castille, and so in a sense either the French queens or the Spanish queens have been the titular Empresses of the Eastern Roman Empire since the 15th century. Another Palaiologian, Manuel Palaiologos, sold his right of succession to Ottoman Sultan Bayazid II (the Ottoman sultans already claim to be the Kaizer-i Rum or Roman emperors); but since there is no such thing as a sultaness because the Ottomans practiced polygamy, there are no Ottoman consorts. Other possible pretenders may be the former Queens of Greece because the Greek monarchy was mainly created in 1832 to be the successor of the Byzantine Empire. The former Queens of Italy could be another claimant since their husband's were one of the only European monarchs to effectively hold the city of Rome, the seat of the Roman Empire since its beginning. 
Neither the Empresses of Russia, the Queens of France, the Queens of Spain, the Queens of Italy or the Queens of the Hellenes claimed any sort of Roman titles and the claimants that clearly made the most point by using the word "Roman" in their title, the Holy Roman Empresses and the Queens of the Romans, ceased their claim upon the dissolution the empire in 1806. Currently the consorts of five of these states are pretenders in their own countries, themselves, and the current Queen of Spain claims no Roman titles. The status of the current pretenders to the Byzantine successor states of Trebizond, Epirus, and Nicaea are unclear much less their spouses; the despots of Morea became the Byzantine emperors (in exile) in 1453.