History of the Roman Empire
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395, he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the West, with his capital in Milan and later Ravenna. The Roman state would continue to have two different emperors with different seats of power throughout the 5th century, though the Eastern Romans considered themselves to be the only ones who were fully Roman. Latin was used in official writings as much as, if not more than, Greek and the two halves were nominally, culturally and historically, if not politically, the same state.
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.