Duny Had Been Cursed at the Age of 13 by a Mage Hired by a Usurper of the Nilfgaardian Throne. Duny's Real Father, Fergus Var Emreis, Had Refused to Cooperate...
Duny had been cursed at the age of 13 by a mage hired by a usurper of the Nilfgaardian throne. Duny's real father, Fergus var Emreis, had refused to cooperate with the plot and so was tortured but this did not break him, so the usurpers decided to get at the emperor through his son. This is where the curse came in.
Who cursed Emhyr?
In books Emhyr's father was murdered and Emhyr himself was cursed into a monster by an usurper to take over Nilfgaardian throne. Emhyr married Pavetta, princess of Cintra what resulted in birth of Ciri. The curse was lifted thanks to Geralt of Rivia.
As part of the coup, the usurper had a sorcerer curse Emhyr, resulting in him turning into an anthropomorphic hedgehog during the day and back into his human form at night. After taking on the name Duny, Urcheon of Erlenwald, Emhyr happened upon the injured King Roegner of Cintra in the woods and saved his life.