Illegitimate children of noble blood are more common than you'd think.
When a nobleman or noblewoman commits adultery and a child is born, that child is usually sent off to a monastery or an orphanage. If the affair partner is of low birth, the child is more often than not abandoned in the streets, left to starve or to grow up into a bandit.
If anything, the Duchy of Beren treats illegitimate children 'relatively' generously. In the empire's east and in France, the word for bastard doubles as a curse, and across the sea in England, bastards are treated no differently from violent criminals.
When England conscripts men for its navy, they are the first to be taken.
The reason illegitimate children came to be treated this way is simple. A child not born to a proper couple joined under the Lord's blessing is scorned for having come into the world without it.
