Merlin_4x09

Arthur looked at his manservant, his face pale and cold. "You saw them, Merlin. You saw her eyes."

"And Camelot will fall with him," Morgana replied, looking toward the castle, her vision of a kingdom ruled by magic now within reach. Merlin_4x09

where Arthur finds out about Merlin's magic? Arthur looked at his manservant, his face pale and cold

The next morning, Arthur was banished to a life of sorrow, riding toward the borders of his kingdom. He looked at his hand, still feeling the coldness of the bracelet. But in the saddlebag, hidden beneath his armor, he found a small, white flower—a Valeriane , the flower he had once given to Gwen. where Arthur finds out about Merlin's magic

Highlights her success in using Lancelot, as mentioned in zahrawithaz's review.

However, in the heart of the woods, a different kind of magic stirred. The spirit of the true Lancelot, momentarily freed from Morgana's control by the strength of his own love for Guinevere, managed to whisper to Merlin in a dream.