Russell T Davies says... This new Doctor is absolutely NOT a conman. I had to wrestle for a long time with bringing these two characters together. Specifically - why don't they recognise each other? The Doctor has clearly said in the past that he can sense other Time Lords, so that even the Master had to be hidden in human form. But then Time Crash came to my rescue - thank you, Steven Moffat! Because in that, the Fifth Doctor very clearly doesn't recognise the Tenth Doctor, even when he's standing in the TARDIS.
Which then suggested to me that Time Lords are now very good at spotting each other.... except for future versions of themselves! Theres obviously some sort of Blinovitch Effect at work, or something. And that simple idea of Steven's opened up this whole plot for me and allowed me to write it.
Of course, there's then the mystery of why David Morrisseys Doctor doesn't recognise the Tenth, but thats the point - as you'll see, the whole story focuses on that. What terrible things have happened, to make him forget?
RTD also confirms that next years second special will be shot outside the UK!