The New 'Doctor'

The New 'Doctor' was a supposed incarnation of The Doctor introduced during the episode Crooked Future, where The Tenth Doctor stumbles upon the Nain Rogue and is put into some form of hallucination where he is almost driven to suicide. The New 'Doctor' shows up as the main driving force of The Doctor's suicide, and ultimately fails when The Doctor catches on that all of it wasn't real, and that this incarnation wasn't him, nor his future, but an embodiment of his fears.

It was led to believe that this was to be the next incarnation of The Doctor following the Tenth Doctor, but this was proven to be false.