The Doctor got up quicker than seemed possible and ran over to the girl. He raised his hand to her cheek and whispered in a hoarse voice, "Jenny?"
She flinched away from his touch and pulled the gun from the strap that went across her body.
"Who are you? You're not the Doctor. What have you done with him?"
He stared down the barrel of her gun and her ice cold glare yet still leaned towards her.
"Jenny, it's me. I am the Doctor. Timelords have a way of cheating death sweetheart, our molecules regenerate and we become new people. When you got shot and didn't regenerate I thought... You know... I never would've left you if I'd known."
Tears had become slipping down his cheek and Jenny dropped her gun and threw her arms around him. His sincerity left no doubt in her mind that he was telling the truth. It didn't matter if it didn't make sense, she was just glad to be in her father's warm embrace again.
Clara, who had been watching their encounter intently cleared her throat and waited till the Doctor turned around to question him.
"I'm sorry, did she say 'daddy'? You have a daughter?! But how?"
He smiled and put his hand on the small of his daughter's back and led her forward towards the other woman.
"Clara Oswald, meet Jenny. Made from my cells and born from a machine. She's my daughter. And she's just brilliant."
Jenny smiled up at him brightly and turned to Clara. As they exchanged pleasantries the Doctor's mind whirled with questions and, of course, some extra regeneration energy.
"Jenny, how did you find me? And why now?"
She gestured for them to sit down on the grate of the tardis floor and took a deep breath before explaining.
"After you left and I woke up, I stole myself an escape pod. I had planets to save and a whole lot of running to do so don't give me that look. Anyways, I had been getting dreams every night. Dreams of a crack and I would hear your voice. Except it was the voice of who you were when I was born. And it kept saying 'find him'. That's what confused me. If it were you it should've said 'find me'. Well it was enough for me to try to track you down. I met some man at a bar on the moon, a captain he was, lovely man, and he said he knew you. Also said something about a crack and a message. So I got back in my escape pod and came here."
The Doctor mulled over her story and suddenly became very still and pale.
"There is a crack in the universes that can allow things through, and there is a man in one of them who is a version of that me. And if he's talking to you, there is a 99% chance that this is very not good."
Clara rested a hand on his forearm to try to calm him down as she asked in a quiet, but sturdy voice, "How not good?"
He buried his face in his hands and said, "Imagine we're in Pompeii. And it's volcano day."