The truth is not quite as out there. Saint George received a blessed sword from a man who was not quite a man. Saint George later in life assumed that the man was a vampire, but he never had any proof.
St. George wandered the countryside, facing off against the Unseen who were terrorizing people in one on one combat. He seemed blessed, or protected, as he did what no other Norm before or since was able to.
Eventually he heard about a Dragon terrorizing a small town in Libya. Arriving, he found the dragon sleeping in its inhuman form. He slew it without a thought or remorse.
The other Dragons in the area had finally had enough of the dragon themselves, and were about to deal with the beast. Seeing St. George with his bloody weapon, they realized that they owed the man a debt.
When the families of the Unseen he had killed all across Europe came to exact revenge upon the man, the Dragons protected him, declaring that he and his offspring were off limites to all retribution for St. George's acts.