A/N: Takes place at the very end of 1x4 The Poisoned Chalice. Told from Gaius' point of view.
He first realizes it when he should be overjoyed. Gwen is there as well, truly and innocently overjoyed because she does not realize. She has not read the prophesies. She doesn't understand who her friend is supposed to be. What he is supposed to do. His destiny. But, in the end, had he? His boy had died. The evidence was irrefutable. Despite their best attempts, despite Arthur risking his life and defying his father Merlin had died.
Yes, Merlin was dead. And then he wasn't. And it is then that Gaius first has a real inkling as to what it means to be Emrys. To lay down everything for the King. To be literally incapable of leaving one's destiny, though death may bar the way.
He should be overjoyed that his boy is laughing, his heart is beating and his eyes are so, so alive. And so he smiles. But inside he is only just realizing what the boy he had come to call 'son' will go through, must go through, and truly? All he wants to do is weep.