Merlin didn't mean to, honestly. He would never purposefully cast an enchantment at Arthur, however sometimes his magic gets ahead of its self.
And the thing is, Merlin felt his magic stir, but magic sometimes just stirs, right? So he thought nothing of it. Told himself, no, you didn't just cast a truth speaking spell on the crown Prince of Camelot and let Arthur walk past him and out of the room without a second thought about it.
Oh, was Merlin ever wrong.
Merlin notices at dinner. Arthur sits down, takes one look across the table and breaks out in a fit of laughter, saying, "honestly Morgana, don't ever attempt that hair do again."
Morgana gasps and Uther kicks Arthur under the table, but it seems to have no effect, Arthur just keeps on going, "I mean this in the rudest way possible, Morgana, your hair do is the ugliest thing I've probably ever seen."
Just as Morgana finishes gaping, she opens her mouth to speak, only then Gwen walks in the room and Arthur's at it again, "Guinevere," he says rather too warmly, "Now there's the prettiest girl in all Camelot. Honestly Morgana, you must have her help you next time."
Gwen gapes just as Morgana had, only she's blushing fiercely, she curtsies and strides off to take her place behind Morgana. Why Arthur then feels it necessary to continue is beyond Merlin, but of course he does, "don't go getting a big head now, you're still not the prettiest person in Camelot. Merlin has you beat by a long shot."
Yes. This is definitely going to be bad.
"Arthur!" Uther declares as his fist slams into the table, "Have you lost all appropriateness?"
"No father," Arthur laughs as if that's the most absurd thing he's ever heard, "I know what's appropriate. I know that hair do, for one, is not. I know me thinking Gwen would make a perfect Queen isn't." Uther's mouth opens and Merlin can almost feel the word sorcery about to slip out, but Arthur keeps blabbing on, loudly, "I also know it isn't appropriate for me to watch Merlin's arse every time he walks out of a room and think about—"
The pitcher Merlin's holding falls to the floor with a loud crash, and suddenly he finds himself doing two things he never thought he would- grabbing Arthur's stupid head, slamming a hand over his mouth to shut him up, and looking straight at Uther, saying, "this must be some kind of sorcery."
Of course Uther believes Merlin and tells him to go fetch Gaius immediately.
Uther doesn't seem to suspect Merlin, however once they're back in Gaius's chambers, free from everybody's eyes, Gaius slaps him hard on the back of the head.
And suddenly Merlin is glad Uther ordered him to stay with Arthur at all times and make sure he doesn't leave his chambers. Grabbing a change of clothes, Merlin quickly hurries off. Managing only to catch a glimpse of 'the eyebrow' and hearing Gaius yell, "Fix it!" as he shut the door.
Merlin's stomach is physically starting to hurt he's been laughing so hard. Merlin always thought Arthur was the type of person who spoke what was on his mind, but no. The Prince has quite a few opinions Merlin was never aware of. A lot of opinions about the knights, especially . . .
"Honestly!" Arthur's laughing along with Merlin now, "Sir Gawaine should not even be allowed within ten feet of a mace! I swear, he's clumsier with that damn weapon than you are at everything . . . but not in the cute way."
Merlin tries, he really tries not to blush, but he can't help it.
"And Leon! Oh don't get me started on Leon . . . I could go on forever about the time he thought it wise to grow a beard . . . no. Not wise at all, Sir Leon."
Merlin doubles over with laughter, and nearly falls out of his chair.
Things are good and well until Arthur feels it necessary to bring up how pretty Merlin is again.
"It's not fair," Arthur starts as he walks towards his bed. Merlin just helped him into his sleep wear, "I'm the Prince and I should be allow to have the prettiest person in my bed with me."
Merlin blushes but says, "don't be ridiculous, Arthur."
Because honestly, maybe Merlin accidentally cast a love/truth spell. Arthur has never once voiced anything of these sorts.
"No, I'm serious Merlin, I think about asking you every night . . . but you're the only person who will refuse me . . . I know this . . . so I always stop myself."
"You are going to be very mad at yourself once this spell wares off."
"Only if you don't get into bed with me," Arthur tries.
"You're not in your right mind—"
"I know what I'm saying! Gods, I'm not a child, Merlin. I know what I want . . . it's what I've always wanted. The only reason I would be mad is if I said all these things just to find out my deepest fear."
"And what's that?"
"That you don't love me like I love you."
Merlin wakes wrapped in a tight embrace.