"Your Doctor might be here twice over," he supplied. "Then again ... maybe not. It's hard to say. The timelines have gone all wrong, but there don't seem to be any lasting effects. I don't remember Rose or Martha or Donna having been sidetracked. I'd wager that your Doctor doesn't remember ever being here."
The Doctor set his cup down and pushed it away, then leaned back in his chair and stared up at the ceiling as though there were answers to be found overhead. "I was supposed to die. There was a prophecy. A fixed point in time, maybe. 'He will knock four times.' I thought it meant the Master ... but it was Wilf, instead. Donna's grandfather."