The Monsterslayer is a Child?

The king and his maester stood before the site of the battle. The battle had already been won for them, and the monster lay prone on the battlefield, motionless even in the braying winds. 

"A child slew the monster?" the king asked.

"By all accounts it was, my lord," replied his maester, who was known as the wisest man in all the lands.

"But that is impossible."

"That is indeed what it should be, but all facts point to that. There was no trace of a wound on the great beast, save a small injury matching that weapon wielded by the young one."

"And that fell the beast?"

"It would appear so, my lord."

"But our great armies failed to match it in battle, and were destroyed!"

"That too is true, my lord, but there are some things beyond mortal reasoning."

"Beyond mortal reasoning? Hold on, don't tell me this is one of those bullshit legends- you know, no man of woman born shall blah blah blah. This child isn't a man."

"I hardly think that is it, my lord. We did try arming a hundred younglings, of various ages and genders, and sending them into battle against the beast. The results were... unsatisfactory, and certainly did affect your approval ratings. What is fortunate, though, is that this is not a democracy."

"Could the fact that he was alone have influenced the outcome of the battle?"

"You are referring to what the Easterners refer to as the conservation of ninja strength? A ludicrous theory, though in our desperation we did attempt it. Several waves of men (and sometimes children) were sent to assault the creature, and we varied the number in each wave by powers of two, starting with five-hundred-and-twelve and finally ending with a lone champion. Again, the results were appalling, though I am glad to report that your manpower bills for the subsequent months will be substantially reduced."

"I suppose there are silver linings to every cloud. Did you notice the weapon the child was wielding? Could that be the key? Perhaps it was previously intractably encased in stone, or was gifted to him by some watery wrench?"

"Pardon me for failing to mention this, my lord, but the wound was inflicted by a finger poke, which if you forgive me for making the assumption, is unlikely to be supernaturally gifted. On later inspection, his finger was not found to have vorpal properties."

"That hardly clarifies matters, does it? This is an important mystery crucial to the survival of the realm, and it must be resolved!"

"I do have a theory of sorts, but it will take some time to research."

"Speak, noble maester."

"What if the child was a mere agent of chance? It is considered very unlikely, if not impossible, for a single person to win the lottery, but all the same someone will win the lottery. By this learned hypothesis, it is clear that this child, which we have shown have no advantage or talent to beastslaying, merely benefited from being near the beast when it expired naturally."

"Expired naturally?"

"Yes, my lord. It is not unheard of for foreign, or even alien, invaders to succumb to all manners of natural deaths. One might even say it died to a bacterial infection."

"That is heresy! We have just barely researched the miasma theory, and I will not have a maester of the realm proclaim the blasphemous theory of germs!"

"Quite right, my lord."

"It appears that we have, again, come to no conclusion. It is most unsatisfactory, but there is no other possibility. Perhaps this is yet another contrived scenario proposed by some odd god to test the wits of mortal men."

"Quite right, my lord, quite right."