Spoilers alert.
So in light novel, vol 16 cap 05. Its explain that Albert Waldestein was the last Heroe in history for repelling the Black Dragon (taking his eye in exchange of his life), it also state that Albert fought that battle alone, and was after that the gods come to our world (1000 years ago).
But Hermes and all the intro in the series said that Zeus and Hera familia were the ones that fought the Black dragon and lost.
So, the dragon has been fought twice?, Albert is Aiz father?, and Albert didnt had a Falna?