He felt so old. Standing in front of the mirror, twisting this way and that to see every square inch of himself, the Doctor raked his body with an uncompromising eye. He took in every scar, every freckle, every spot on his body, seeing some of them bend and triple over themselves in his mind's eye. He remembered what every body felt like, how it felt to move in his old skin. Each new one felt like a fresh new case, a new layer that swaddled him.
This skin had no holes. His last one had had holes, huge ones, gaping ones, that others could poke at and press. They could get reactions out of him even when he hadn't wanted to. The one before that was scar tissue, soft and pink and new but won over years of battle and stained by war. This skin had no holes, and it was thick. The Doctor felt slow in this one, like he couldn't feel it until the emotion had died already in his throat.
So he turned and twisted around himself, bending his fingers and folding his arms over his chest. He tried to ripple his own skin, to find bumps of skeleton, to discover hidden maps of muscle.
Everything looked so human.
And then he shut his eyes, pressing two hands to his chest. Two heartbeats resonated deep inside himself, beating golden-red blood through silver veins. He could imagine the inside of a Time Lord, with all their colors and swirls and patterns in their very bones. They etched out his age in threads of blood and sinew. 907, 908, 909, 910, 911… Suddenly, with a shudder, he jerked his hands away and leaned in closer to the glass, his breath fogging it up.
He felt so, so old.
Hunching over, he felt his body crumple. Skin sagged and skin pulled too taut and he felt like a monster so he bared his teeth in a grin. Monsters lived for millennia, for generations, for centuries, for a day. He'd outlived them all. He stuck his tongue out. He could feel his vertebrae attempt to escape muscle and sinew and skin, reaching out to taste air. He shut his eyes, biting the inside of his cheek again. He tasted blood like iron and hemoglobin. No life. Not in his blood any more.
So, so old.
And suddenly he felt a pair of arms snake around his middle, straightening his back. The Doctor's eyes flew open and he looked down to see tan skin and familiar hands holding him, one finger tracing the lazy loops of circular Gallifreyan on his skin.
When she touched him, he felt new. The old dust that had settled on his bones long ago melted, leaving gooey drips along his insides. They painted swirls and colors that he never knew existed. The Doctor didn't know if it was just her regenerations singing out to her again, clamoring to be reunited with their soul, or whether it was her regenerations singing out to him, clamoring to show him just how loved he was to have them.
With her, eleven bodies became one.
Turning around, the Doctor scooped River into a giant hug, peppering her shoulder with kisses.
With her, he felt so new.