This is basically what it says in the title. 5 ways that Merlin's magic was discovered. It contains spoilers for the first season and is merlin/arthur. I do not own Merlin or any of the characters so please do not sue me. I don't have anything to give you.
1)"It was you who used magic wasn't it? Not Will." yelled Arthur to Merlin fury and disappointment etched across his features. He wasn't afraid of Merlin, he was a idoit even with magic Arthur didn't believe that Merlin was capable of doing anything to harm Camelot or any one in it. His mental affliction made sure of that. The problem was that Merlin didn't tell him, didn't trust him enough and believed him of being capable of handing over to the King to be executed. That hurt much more than it should. Even though Arthur was horrible to Merlin he liked to think that the where friends, even hoped that it would develop into more than that. Though with Merlin's obvious distrust of Arthur meant that it was unlikely. "I can't believe you kept this from me and then allowed Will to take the blame that. Was it so important keeping your secret from me that you let you best friend die" he hissed at Merlin clearly not caring about how much his words were hurting Merlin and ignoring the fact that he knew it wasn't true. Arthur stalked off content to leave Merlin crying to himself even knowing how much he hurt him. Arthur knew it was wrong but at that moment all he saw was his pain.
2) Merlin hated hunting. He couldn't see how anyone could enjoy killing innocent animals. When they did it for food Merlin understood but he couldn't understand why anyone would do it for fun. He almost had thought that Arthur had learnt his lesson after what had happened with the unicorn. But obviously he didn't, not that Merlin was suprised. This was Arthur the royal prat he was talking about.
A bear seemed to appear out of nowhere. Arthur had no chance to react the bear attacked. Merlin had no choice, it was the only way to save Arthur. For a brief second doubts about using magic in front of Arthur popped into his mind but he quickly dismissed them. He needed to save Arthur and if it got him killed it didn't matter he was just a servant and Arthur was the prince. It was much more important for Arthur to live so much that Merlin was willing to risk being executed for it. "Contego" he yelled out, his arm stretched out towards Arthur. Though the gold Merlin somehow knew that Arthur was most likely to be staring at him in shock. "Incendia" he chanted towards the bear wanting to scare him away but not to kill it. Once the bear had gone Merlin reluctantly returned his attention to Arthur.
"You're a sorceror" Arthur started not looking at Merlin. Merlin quickly started to try to explain to Arthur that he wasn't evil and that he had only used his magic to help those in Camelot especially Arthur himself. Arthur hussed Merlin, he already knew that Merlin wouldn't hurt anyone."It's okay, I believe you he whispered as he embraced Merlin happy that he figured out the mystery that was Merlin though Arthur couldn't help but think that Merlin was strange even for a warlock,
3) "You're a warlock aren't you" Arthur hissed unable to keep the disgust out of his voice. " You worthless traitor" he yelled at Merlin pushing the young sorceror away from him too angry to notice how Merlin didn't use magic against him even to protect himself. Arthur knew he should take Merlin too his father especially since he knew what evil those who used magic had inside of them. Even with all of the lies and the knowledge that magic was evil which Arthur had been taught since birth he couldn't let Merlin get killed. But that didn't mean that he wanted to spend anytime with the traitor or that he had forgiven him in any way or form. "Get out of Camelot" he demanded "or I'll hand you over to be executed". Merlin gave him a sad look look before all but running from the room. He had hoped that Arthur would react better. He thought that Arthur knew him and wouldn't believe him to want to harm Arthur or any of Camelot. It was too much to hope that Arthur would think of all the times he had saved his life. As Merlin left Camelot and his prince behind he couldn't help but wonder about how the dragon had gotten it so wrong. He had failed, he just hoped the consequences wouldn't be too dire.
4) Arthur pushed Merlin back towards his bed. Pressing his lips to anyhwhere he could reach. Merlins lips, nose and even his neck. Normally Merlin hated to be pushed around especially by the royal prat Arthur, but he had dreamed about this happening so many times and didn't want it to stop. Arthur pushed Merlin back onto the bed before staddling him. Merlin didn't think it was possible to be so happy. He had finally gotten what he had wanted. Arthur.
As Arthur latched on to his pulse point Merlin could feel the magic bubbling inside of him. Quickly closing his eyes hoping that Arthur didn't notice his eyes turning gold he tried to push the magic back. "Open your eyes" Arthur whispered huskily into Merlin's eye before starting to nibble on his earlobe. Merlin slowly obeyed afraid about how Arthur would react to the magic that was burning behind his eyes trying so hard to force it's way out. Arthur gasped at the gold eyes that had replaced his manservants gorgeous blue. Slowly leaning forward to whisper something un Merlin's ear, Merlin felt his heart drop. This would be where the prince either sent him away from Camelot. Smiling Arthur pressed his mouth to Merlin's ear " I already knew you idiot" he whispered and Merlin felt his heart soar. He had hated keeping secrets from Arthur annd was glad he no longer had to. Smiling Merlin leant forward catching Arthur's mouth in a kiss.
5) "I'm a sorceror" Merlin declared to Arthur hoping that this time his claims would be taken seriously. Arthur looked at him for a brief second before bursting out in laughing. "Merlin you idiot" he started between his hysterical laughter " did you really think that you the idiot that you are could keep such a secret from me. I knew the whole time". Seeing the shock on Merlin's face only seemed to make Arthur laugh more. Merlin couldn't believe that he had been so obvious in using his magic. He had thought that he had kept it well hiden. Merlin just couldn't help but wouldn't how many people now knew his secret. Mistaking Merlin's worry Arthur quickly whispered that he wouldn't tell anyone else and that he knew that Merlin wasn't evil even if he had magic. Notcing that the haunted look stayed in Merlin's eyes he wrapped his arms around Merlin gently kissing his hair wondering what he could do show Merlin that he was safe.