AN: so this is somewhat how I pictured Eleven's regeneration to be, but it does have parts of what acctually happened in the episode.
Clara stepped into the TARDIS "where is he? Is he alright?" She thought "What face did he end up with?"
The doctor's coat and his dark bowtie was lying on the floor. There was some fishfingers and custard in a bowl on the console.
"Was it too late? Is he dead?" She thought, but then she heard footsteps from the stairs, and there he was. Standing right there in front of her. Young again. She could see his beautiful brown hair again. Clara didn't even try to stop the bright smile on her face, allowing her dimples to show.
"You're not dead. You - you haven't even changed your face. And you seriously talked about tens vanity issues." She said, "This is the reset. This body is dying, I can feel it", Clara's smile faded. She also noticed what he was wearing. A light brown coat, a blue shirt and topped with his signature red bowtie. She remembered this outfit from her life as Oswin and generally, just being in his timestream. It's what he wore before he lost Amy and Rory. His best friends. It was like he wanted to give his all to the last minutes of the eleventh hour.
But the long song was ending. Clara could hear the song in her head. Rest now my warrior. Rest now your hardship is over. Live. Wake up. Wake up and let the cloak of light cling to your bones. Cling to your bones.
The doctor looked at Clara. His Clara. Tears fell from her beautiful chocolate-coloured eyes. His hands started to glow just a little bit. He felt a sudden pain in his hearts and fell down on his knees. Clara went forwards "NO!" He said "I will regenerate any second now, there's going to be a big bang, and maybe even fire. Step back, don't come any closer."
Clara obeyed although she wanted desperately to hold him. She remembered one of the echoes. The one who had been a Time Lady. She remembered what regeneration felt like, sometimes it hurt. A lot. She didn't want this for him, but she knew she couldn't stop it.
The doctor looked down at his hands. They started to glow brighter. He could see the yellow light on his skin so clearly now. It clinged to his bones and it ran through his blood. When he looked up again, he thought for a moment, that he had died and for some strange reason, ended up in heaven.
Because they were standing there, right behind his impossible girl. The girl who waited and the last centurion. Amy smiled at him, so did Rory. Rory held the hand of a little girl with Amy's eyes and Rory's light brown hair, and the doctor knew it was Melody. Melody Pond if he hadn't ruined everything.
He sighed "oh, silly old doctor." He said. He was certain his face was glowing too, now. Clara reached out her hand. The doctor smiled at her. Then at Rory, followed by Melody and lastly at Amy who said, "raggedy mad. My raggedy man. Goodbye." The last tears of his green eyes, fell from his cheeks.
"Geronimo" he whispered. And that was the last words of the raggedy, eleventh doctor. The yellow light shone brightly, and it was like he caught fire. The long song is over now.