Link casts the necessary spell on him quick enough that he doesn't notice anything is wrong.

With a brief effort of will Link cast the spell that Zelda was trying to use, and in a few seconds he seemed to look like his old self again. Was he going to notice the fact that the magic came from her, and not himself? He looked at her, as though he had something to tell her, then shook something off and left. It looked as though he hadn't noticed a thing. Link spent the majority of her day reading, excited to see what would become of her captor next. When Zelda finally returned home after a long day of being a ruler...