Another one for The Crystal Cave.
"I had to stop the future. I had to stop Morgana killing Uther."
Something Much Worse
It wasn't Uther's death which frightened him.
Of course, Uther was the king, and more than that, he was a person, with a soul like any other. Merlin could hardly bring himself to wish for the painful death of another, no matter what he had done or how little regret he showed for it. Even so, the vision of Morgana's killing the king was not truly shocking, for he knew, even then, deep inside himself, that she would someday. Seeing it was not enough to send him scrambling for a way to stop it, as he desperately did.
Gaius tried to calm him, telling him not to worry so much, for whatever future he saw in the crystals was yet unstable, easily manipulated.
He could not be calmed. He had seen it, that one vision which had been mere flashes between more prominent ones, more subtle and distant than the others picturing Uther's death.
He could not keep from thinking that, if he could alter the immediate future and keep Morgana from killing Uther, then, decades from now, he might also stop Mordred from slaying Arthur on that inevitable battlefield.