Previous Doctor (Seven Keys to Doomsday)

A previous Doctor regenerated into a new incarnation after being attacked on the planet Karn. (AUDIO: Seven Keys to Doomsday)

Behind the scenes

 * In the play on which the audio story is based, the incarnation who regenerates into the story's main Doctor is Jon Pertwee's Third Doctor. The play is not, however, considered a valid source on this Wiki, and as for the audio story itself, Nicholas Briggs seems to make little effort to sound like Jon Pertwee. As for Briggs himself, it is perhaps noteworthy that he portrayed an unlicensed incarnation of the Doctor in several other audio plays, namely the Audio Visuals.