Original: Another less famous "conquest" took place in 1503, when Andreas Paleologus, de jure Emperor of the Eastern Roman Empire, left Ferdinand and Isabella as heirs to the empire, thus Ferdinand became de jure Imperator Constantinopolitanus.
Simplified: Another less famous "conquest" took place in 1502, when Andreas Paleologus, de jure Emperor of the Eastern Roman Empire, left Ferdinand and Isabella as heirs to the empire, thus Ferdinand became de jure Roman Emperor.