The first time Rilian sees the Lady of the Green Kirtle, she scares him nearly to death. Because of course he is looking for a snake, so he can avenge his mother's death, and he doesn't expect to see any humans at all in his quest, not up in these quiet northern woods.
His father has told him it would be no use to chase after a witless snake, that killing it would not bring his mother back, or give Rilian the peace that he seeks. But Rilian is young and angry and his heart aches at the loss of his mother. So he ignores his father's words, and every day, rides up among the northern marches, seeking his mother's killer, the poisonous green serpent that haunts his dreams.
So when he sees a beautiful woman dressed all in green, sitting on the edge of the fountain in the very same glade where his mother died, he is so startled he nearly falls off his horse. She is the most beautiful woman he's ever seen, and it's like she's appeared out of nowhere - one moment he thought he caught a glimpse of the snake, and the next, the Lady is sitting there, her green gown shimmering in the sun. Rilian wonders if she is perhaps a fairy, or one the shapeshifters of legend that are still rumored to live in the north.
But then she greets him in a sweet voice, and he forgets all about fairies and shapeshifters. The Lady asks his name and his business here in the north. "I have seen you riding about for days, armed as if expecting a battle, and I am curious, young sir."
If Rilian weren't so miserable, he might remember all that he has been taught, and how dangerous it is to give your name to a creature you don't know. But he is already enchanted by the Lady's voice, and he slides off his horse and bows low to her, and introduces himself as Prince Rilian of Narnia.
And when she takes his hand, he is already lost.