Books
The Foundling Prince
A. N. (Aleksandr Nikolaevich) Afanas'ev
Adapt

Once upon a time, there was a Tsar and a Tsaritsa who had only one son. One day, the Tsar had to leave home, and while he was away, a terrible thing happened: the young prince disappeared. They searched everywhere for him, even dragging the ponds, but not a trace or sound of him could be found. Fifteen years passed, and at last the Tsar received news that in a certain village, a peasant had found a child who was astonishingly beautiful and clever.
The Tsar ordered the peasant to be brought to him immediately. When the peasant arrived, the Tsar questioned him about where he had found the boy. The peasant explained that he had found him fifteen years ago in a corn-kiln, dressed in strange and rich clothing, and by every sign, the boy was the Tsar's own son.
So the Tsar told the peasant, "Tell your foundling that he must come to me neither naked nor dressed, neither on foot nor on horseback, neither by day nor by night, neither in the courtyard nor in the street."
The peasant went home, weeping, and relayed the Tsar's message to the boy. How could this ever be done?
But the boy replied, "That is easy enough; I can solve this riddle."
So he undressed completely, put a net over himself, and climbed onto a goat. He approached the Tsar's palace at twilight and positioned the goat at the gate, so that the goat's front legs were inside the courtyard and its back legs were in the street.

When the Tsar saw this, he became convinced and said, "This must be my son!"