Geralt of Rivia helped Emhyr var Emreis (using the alias Duny) from him being killed and lifting his curse. Duny filled with gratitude was willing to give the Witcher any reward he asked. Geralt asked for the Law of Surprise, an oath binding magical law that has unexpected results. Turns out Dunys bride Pavette was pregnant when this oath was made forever intertwining the fate of the baby; Princess Cirilla Fiona Elen Riannon, and Geralt forever.