The pain of regeneration stole his breath, quite literally. It was worse than dying, being rewritten this way. He knew it was what was supposed to happen, the Time Lord's way of cheating death, but for a moment he struggled against it. He wasn't ready to go, and yet he knew he wasn't really leaving. He'd stay on, he'd just be… different. The pain intensified, erasing all thoughts, and he gave up the struggle.
The pain left as quickly as it had come. One second he was in agony and the next… nothing. No, not nothing. He was reclined in something soft yet supportive which swayed slightly. The air was warm and a gentle breeze brought the sweet smell of freshly-cut grass to his nose. The Doctor opened his eyes slowly and found he was laying in a hammock, staring up at the branches of a heavily-leafed tree.
"Hello, Sweetie." The Doctor started, turning toward the voice, and found himself looking at his wife. River beamed at him, her smile a mixture of joy and triumph. She was sitting in a lawn chair, dressed in flowing white robes, with her golden mane of hair tumbling in wild abandon past her shoulders. She was holding a champagne flute in one hand. She reached out with the other to take hold of one of the Doctor's.
"Wha… what? How? Where?" River's smile widened.
"CAL, of course," she said.
"But… but how?"
"Oh come now. She was born to save you, remember?"
"Clara."
"With a bit of help from the TARDIS." River lifted the flute to her lips and took a dainty sip. "It turns out I'm as bad at endings as you are, my love."