But the daughter of the castle was by far the most beautiful. Merlin looked at her in great distress, and he thought to himself that anyone would be very lucky if he could sleep with such a maiden. “And if it weren’t for the great love I have for Viviane, my lady love,” he said, “I would be holding her in my arms tonight. But since I cannot have her for myself, I’ll see that King Ban will have her.”

Then he cast a spell with little ado, and as soon as he had done it, King Ban and Agravadain’s daughter fell deeply in love with each other.

Vulgate Merlin