The line of perfectly placed heels in the bottom of his personal section of the wardrobe should have been a clue, but it never really occurred to him to wonder before now.
She tosses him the heels she'd been wearing when they had landed on Alfava Metraxis. He scrambles to catch them and she grins. "Put those in the bottom of the wardrobe with the rest won't you sweetie? I'll get them the next time I need them." And with those words she spins back around and disappears back into the portable building the clerics had brought with them.
Amy was never going to let him live that one down, evidenced by the giggle and the comment she delivers just before he's out of earshot on his way to put the shoes into the TARDIS. "Oh, she is so Mrs. Future Doctor, and you are so whipped already." He doesn’t comment back. He walks through the corridors and into the wardrobe to deposit the shoes into the row.
There are all sorts of pairs there, sturdy boots and some that look like one might fall in them, trainers and flats, wedges and sinful looking heels much like the red ones he’d just dropped into the line. He takes a moment to wonder what else there might be if he really looked. He doesn’t really spend much time in here, not unless he can’t get away with his usual wardrobe choice, and even then he sometimes doesn’t bother.
He rifles through the rack curiously. There are his jackets and suits of course, garish things and frilly things and black leather from his previous regenerations. Though several spaces over he notices other things. A khaki green dress with a zipper, a few pairs of more practical looking things, jodhpurs, vests, both lighter and heavier jackets. There's a green dress that shimmers when the light hits it and the minute he spots the bow on the front he decides it’s more than beautiful. It scares him to think what these things mean and he shoves the hangars back together. In his haste to return to Amy he stumbles and notices that there is a dresser he’s never used before.
It’s unremarkable really, except that he spots that a drawer has been left slightly open. He never can resist a curiosity, it will only take a moment. He reaches out and opens the top drawer, sliding it open and peeking inside. It smells of her. River’s perfume wafts up and it’s like she’s standing next to him. It’s mostly pieces of jewelry, a biro pen, three lipsticks, a few things he’s never used but recognises as hair accessories.
The second drawer seems to contain a set of keys, a lock pick, and a box that looks suspiciously like a small gun case. He closes the drawer quickly and moves on, wondering how much is spoilers he’s not supposed to see, but it’s his TARDIS so he continues. The next drawer is causes him to blush, is that a-? No, it couldn’t be, but it shaped exactly like... He quickly shoves the drawer closed. He’s about to leave when the curiosity about the rest of it’s contents starts to burn and tugs open the next drawer. Inside are colorful fabrics. Tiny fabrics, sheer things and lace things, and some that are nothing but ribbon. Before he knows it he’s reached inside and lifted up something made of black mesh. Oh, knickers! He drops them quickly and tries to shove them deeper into the drawer.
When he pulls his hand back out, the button of his shirt sleeve has tangled with something that looks like it’s supposed to be a bra but there's not enough of it to actually cover actual breasts, which he knows River has, he’s seen them. Well not seen, felt, earlier on the floor on the console room. He pulls the drawer open to untangle his sleeve and shove things back inside but he’s in too much of a hurry and pulls the drawer too far causing it to fall off it’s tracks. As it drops to the floor and he tries to catch it with the drawer pulls, but only causes it to tip sideways. Suddenly there's a pile of clothing on the floor. Well, he couldn’t call it clothing exactly.
He spends the next five minutes trying very hard not to imagine River Song dressed in any of these things as he is forced to pick up and fold countless pairs of knickers and teddies and corsets and whatever the thing with the leather bits and metal rings had been. When he finally exits the TARDIS again to find both River and Amy he’s sure it’s with a blush still on his face. For a moment he’s sure River can read everything on his face, but she doesn’t say anything out loud. And if Amy or anyone else catches him staring at her later trying not to imagine what sort of knickers shes got on under the clerics uniform, they don’t voice it either.