Uther might initially be shocked. He has always been so against magic, so he could be furious at first. He might feel betrayed by Merlin, whom he has known for a while.
One possibility is that Merlin's revelation of his magic could lead to a change in his relationships. For example, his friends who were previously unaware might react with shock, some with fear and some with acceptance. His enemies, on the other hand, would likely see him as an even greater threat and might plot more vigorously against him.
She might be shocked at first. Given that in the original story Morgana has her own complex relationship with magic, seeing Merlin's magic could stir a mix of emotions in her, like envy or a sense of relief that she's not alone in her magical abilities.
One great aspect of Uther Pendragon and Merlin fanfiction is the exploration of their complex relationship. In the original series, Uther is often at odds with Merlin's magic, but in fanfiction, authors can reimagine their dynamic. For example, some stories might have Uther discover Merlin's magic earlier and instead of persecuting him, learn to accept it due to Merlin's selfless use of magic for the good of Camelot.
The storyline might progress with a lot of drama. People's reactions would be the key factor. If he reveals it to Arthur, for instance, Arthur's response could either make their friendship stronger or break it apart. This would then lead to different paths for Merlin, either having to hide again or standing up against all odds.
One great Merlin Uther fanfiction is 'The King's Regret'. It delves into the complex relationship between Merlin and Uther. It shows how Uther might have reacted differently to Merlin's magic if he had known the truth earlier. Another is 'Uther's Hidden Affection', which explores a more emotional side of Uther towards Merlin, a side that was perhaps masked by his hatred for magic in the original series.
Well, Arthur could feel betrayed at first. He has been brought up to believe that magic is bad, and here his closest friend has been hiding this big secret. However, as he realizes how Merlin has saved his life and the kingdom many times with his magic, he might come to accept it and even see the potential of magic being used for the good of Camelot. For example, Merlin's magic has defeated many enemies secretly, which Arthur might now understand as a necessary protection for the kingdom.
In fanfiction, if Uther finds out Merlin has magic, it could lead to Merlin's immediate arrest. Uther is known for his extreme hatred of magic in the Merlin series. He might see Merlin as a great threat and try to execute him, just as he has done with other magic - users.
It would be very complex. Initially, Uther would be in shock. He has been hunting magic - users, and now his son is one. But he might also feel a sense of protectiveness. Merlin, on the other hand, would be confused and angry at being lied to about his identity. Eventually, they might start to understand each other more. Uther could see the good in Merlin's magic and Merlin could see the reasons behind Uther's actions, even if he doesn't agree with them all.