Written for this prompt:

Arthur/Merlin, Gwen/Lancelot

When Gwen begins to fall for Lancelot, Merlin enchants himself to look like Gwen when Arthur calls for her because he doesn't want his friend to get hurt. Gwen hardly spends any time with Arthur and Merlin's forced to repeat the spell over and over again, making Gwen wonder why Arthur appears to be more in love with her than ever while she's been less affectionate with him.

Arthur eventually finds out the truth and discovers he hasn't been falling all over again for his wife but for Merlin instead.

A/N: This is my first Merlin fic on this site! Beware for all you homophobes, this is Arthur/Merlin slash.

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Chapter 1: Ambiguous Use of Magic

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Arthur watched, his eyes remorseful, as the foreign dignitaries left Camelot, arm in arm. Gwen sat next to him in her throne, elegantly smiling as the couple left. Arthur could tell she was bored out of her mind—this whole "queen" thing just wasn't for her. She would rather be spending her days doing practical things that would visibly benefit the castle, instead of sitting for hours playing the subtle game of politics.

As Arthur sat back down on his own throne, he glanced at Gwen from the corner of his eye. They used to be like those dignitaries, so in love… what had happened? Where was the happiness he imagined that would come after marriage? Where was the joy, the laughter? What had he done wrong that Gwen could hardly stand to be in the same room as him?

Arthur sighed as the guards ushered in another group of visiting nobles. He was at a loss of what to do. Seeing that young couple, a mirror image of himself and Gwen back in the past, it made him crave that intimacy again. He had been content for the past few years to let her fade off into the distance seeing as he no longer felt anything for her either, but now…

He straightened his spine and gave a regal nod as the nobles bowed. No, he was going to win her back. He was going to get back the best relationship of his life; he was going to win his wife's love again.

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Merlin paced anxiously in Gwen's room as he fretted over Arthur's last command. Though he was the Court Sorcerer and Top Advisor of King Arthur's Court, he had somehow landed up as a messenger boy between Arthur and Gwen. Merlin swore that Arthur still treated him like a manservant out of spite. He still wasn't over the fact that Merlin had hidden his magic from him for over three years.

That was besides the point though. Merlin strode back in forth in the middle of Gwen's room. Arthur had called to have dinner with Gwen for the first time in what seemed like years. Merlin knew that Gwen had moved into separate quarters early on in their marriage, and not soon after the two were hardly spending any time together. Of course, outwardly they seemed to be the perfect couple. Arthur often explained how his relationship with Gwen was a matter of politics, but Merlin still didn't get why they had to act one way in public, while being completely different in private.

However, it appeared as though Arthur wanted to rekindle their private relationship. And that was how Merlin was stuck in this dilemma. Gwen had been seeing Lancelot for a few months now, ever since he came back as a full-fledged knight. Merlin knew it wasn't fair to Arthur, but he often saw the looks that passed between Gwen and Lancelot and he couldn't bring himself to break them up. That didn't mean he wanted Arthur to find out about it, though. No, that would totally destroy Arthur. Telling him was out of the question.

But now that Arthur suddenly requested Gwen's presence during dinner—while she was out with Lancelot too!—he didn't know what to do. How was he supposed to make Gwen meet Arthur for dinner if Gwen wasn't even in the castle? A doppelganger? But those were simply physical forms of the person, they didn't actually talk. An illusion? No, if the illusionary Gwen tried to eat, then the food would drop right to the floor and the gig would be up. There had to be some other way…

An idea popped into Merlin's head, but it wasn't one that he was particularly proud or eager of: he could transform into Gwen himself and meet Arthur for dinner, pretending to be her. It was one of the more unscrupulous things he had done with his magic, but it seemed to be the only option…

Merlin sighed to himself. Well, he had done worse for Arthur before. This was just one more thing that Merlin had to do for his best friend.

"Awendednes min feorhbold aet Gwen" he mumbled to himself, running his hand over his body. He could feel the change occurring almost instantly. He watched as his skin darkened, his hands shrunk, and a heavy weight appeared across his chest. He stood uncomfortably in his friend's body, trying not to touch anywhere that would seem inappropriate.

"Alright, I need clothes…" Merlin muttered, wandering over to the cabinet. "Where does she keep her dresses?" Merlin opened the two doors and instantly spotted dresses fit for a dinner with the king.

Now for the hard part… Merlin closed his eyes and slid off his tunic and breeches, trying to keep Gwen's modesty intact. He grappled for the dress, sliding it onto his body. He tentatively fixed it over Gwen's chest, groping his back to tighten the corset. He gave a sigh of relief when it was all said and done. Merlin glanced at himself in the mirror and saw Gwen staring back, all dressed up in a nice, blue evening gown.

"Hello, my name is Gwen." Merlin said to himself in the mirror. He saw Gwen speaking back, but it didn't sound quite right. "I am going to meet my husband, Arthur, for dinner." He said again, trying to match his speech patterns with Gwen's own. That was more like it.

Merlin smoothed down the miniscule wrinkles in his dress and took a deep breath. It was time to go meet Arthur. He desperately hoped this worked, otherwise Arthur might be severely heartbroken.

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A/N: This was supposed to be a one-shot, but I got stuck somewhere along the 3k mark. I'm hoping to be inspired by posting this fic.

And shout-out to all you Abluvion fans who are also Merlin junkies as well! This pairing, and Klaine, are what make up my life right now.