Warning: This article contains spoilers fromThe Witcherseason 3 finale, “The Cost of Chaos.”
That would beFreya Allan’s Princess Cirilla.
Not Geralt, not Yennefer.

Freya Allan’s Ciri in ‘The Witcher’ season 3.Susie Allnutt/Netflix
“The fire draws her in and Falka draws her in… and she basically relinquishes her powers.”
Doing so, however, causes the pure creature to flee from her.
When asked her name, she tells them to call her Falka.

Ciri trapped in the Korath Desert in ‘The Witcher’ season 3.Susie Allnutt/Netflix
It appeared Teryn was cured of this magical tampering but has now clearly succumbed again to dark influence.
“We learned she’s powerful.
Maybe she is the villain of the story.
Maybe it’s to become a villain and to actually destroy the world.”
Geralt, too, goes through a tremendous change by the conclusion of season 3.