Mistress

For the following prompt on Tumblr: "would you be able to do someone little about athos' thoughts when he sees milady as louis' mistress for the first time. we saw him in episode 5 i think seeing them and he literally looked pained but the very first time must of hurt."

Poor Athos doesn't seem to deal very well with seeing Milady with the king, does he? This was a fun prompt to write, though I probably should've rewatched the episode first ...

It's her smile that undoes him in the end.

Not the triumph in it; that is Milady's, and reminds him only that she is a ruthless woman who will stop at nothing to get what she wants. And if that was all, if her expression was merely self-satisfied, then he thinks he might be able to hate her in peace. But there's a wonder there when she thinks no one is watching, as if she cannot quite believe how this has played out, that softens her eyes, and that too is something he knows – and it's something he had thought was his alone, because in that moment her eyes are Anne's, are those of the woman he had loved and wedded and been betrayed by, and he can't decide if it hurts more to think that it had been truth or lie back then.

He should have expected this. He knows the ways of the nobility, that flaunting a mistress is a common enough action for a man of power to take (has seen it, time and again, though the act had never appealed to him even when he had been the Comte de la Fère rather than Athos of the Musketeers), but had perhaps naïvely thought that the king would not be such a fool, when relations with Spain are so tenuous and his marriage is some days all that keeps them from tumbling into war. But Louis has always been a self-absorbed fool, and when the rumour that Milady has been installed in the Louvre reaches his ears, Athos reminds himself that he should not be surprised, and that she means nothing to him.

(It is not the first lie he has told himself about her; it is unlikely to be the last. The ground between them has always been a treacherous space, murky with falsehoods and half-truths and the rare honesty neither of them will ever admit to voicing.)

But she does, she still does, she has meant too much from the beginning and she likely always will, and the sight of her on Louis' arm dazzles him no matter how prepared he thinks he is, because that smile is brighter by far than any of the jewels that bedeck the ladies at court, and he wonders that he is still whole and not flayed bare for them all to see his pain. In that moment he feels raw and exposed, and Porthos' grip on his arm, though meant to steady, only makes it worse. Aramis is watching the Queen, who is watching her husband with a frozen expression, and d'Artagnan is bristling, and Athos feels as if he should say something but the words dry up in his throat.

"Alright?" the bigger man asks, a low rumble. The word fractures something, jolts him out of his paralysis; he grunts a negation and pulls away. The touch is well-meant, and any other time it would ground him and reassure him, but in this moment the warmth of Porthos' hand is one more thing that keeps him open, and he can't –

"I'll see you back at the garrison." It amazes him that the words come out as steady as they do. And though it's clear in the worried look Porthos gives him that he knows something else is amiss, he doesn't push, and if Athos could feel anything other than despair and hurt and bleak rage in that moment, he would appreciate it. Instead he just turns – away from Porthos' worry and d'Artagnan's anger and Aramis' heartache and Anne's blinding smile – and stalks out of the palace.

(Even in the bottom of the bottle, that smile haunts him.)