If you want me to go into depth of how he can actually be of Roman lineage then I could always do that, however only if you, Vita so want me to.
I mean if we follow the time of the Roman empire to it's collapse and to Byzantium then I don't see how no one could survive from a roman lineage, I mean it was the antique, people had children some way or another, people can move from locations as well, from Rome to Greece back to Rome, for example. Not really saying that is the case in our real world, however I don't see why it wouldn't be allowed or possible.