The Doctor was dead. The other time lords tried to save him, but he denied them. It was his time. He's been in his own timeline, he knew this couldn't change. He changed enough Fixed Points in his life, This time he would just let things...happen.
Nobody knew what happened to Time Lords when they died, Some had a few educated guesses, but nobody ever gave them much thought.
As The Doctor went into the light, he felt his skin harden into stone, his features change into a generic, premade shape. He knew immedietly what was happening.
He was turning into a Weeping Angel.
The Doctor felt a strong urge to return to the graveyard, the last place he saw Amelia Pond, his best friend. He had to see her one more time, and with his new form it wouldn't cause her to realise there were two of them there.
He saw Rory looking at his own tombstone and he looked around to see if he could see where the Angel was, the Angel that killed the couple.
He then realised what was happening.
He swished over to Rory, and as heartbreaking as it was, he knew he had to. He touched Rory, sending him back to 1938.
He saw Amy, right in front of him, he couldn't move, but he wanted to sob at the sight of her. How he longed to see her again, but not like this. Not as her second greatest fear, and the thing that kills her.
She was talking to the younger version of himself, then she said "Raggedy Man, Goodbye!" and turned around finally facing his younger self for one last time.
'Goodbye Amelia Pond.' He thought as he touched her gently on the shoulder.