When Merlin turned back to look at Arthur, he looked like his brain might have stopped working. His brows were wrinkled in confusion and he was blinking, as if hoping the movement might get the wheels turning again.
"You.. what?"
It really shouldn't have been that difficult a concept to understand. Time travel was obviously a fact of life. They were in the future, it shouldn't be surprising that people around them came from the future. Still, Arthur was comforted in knowing that his group of people were from the same time period--give or take a month--in their own little bubble. This was a clear violation of the bubble.
Merlin was a father? Arthur had barely gotten used to the idea of Merlin having a girlfriend!