Apparently from whats been said on youtube...is that :
I Quote : The Doctor gets shot by a Dalek and gets split into Paul McGann (8TH Dr) and Christopher Eccleston (9th Dr)..... that would cause a paradox BUT the TARDIS still has some of the properties of a paradox machine so stops the paradox, also we find out about the regeneration from 8th to the 9th Doctor
I am not sure if this is 100% true tho....but that is definately Mr Eccleston in the vid [/QUOTE]
This may be for the "Children in Need" special, so there is MUCH speculation!
Ok..here it is....Christopher is back in the series 4 Finale of Dr Who...