The Doctor (The Death List)

A future incarnation of the Doctor was female. She hid her face behind a mask and wore stilettos. Her cloak spelled the number "13". (PROSE: The Death List)

A day to come
The Twelfth Doctor once gazed at a female mannequin positioned in the doors of the TARDIS as if he held knowledge of his future incarnations. (PROSE: A Good Man)

In a chest containing items belonging to the first twelve incarnations of the Doctor was a handbag belonging to a future female incarnation. (PROSE: Contents)

As an assassin
The Doctor became an undercover assassin that served the King. She became known as the Masked Assassin.

After some time the King decided he wanted the Doctor dead. She ran across the hills and took cover behind a Dalek. After communication between the ranks the King's henchmen eventually contracted the Doctor (under the guise of the Masked Assassin) to kill herself.

The Doctor managed to convince the people to revolt against the King and use democracy instead. After this the Doctor confronted the King where she revealed she was his assassin. She then announced that she had emptied out his slave mines and that all his guards had fled. The people had spoken and were on their way with pitchforks. The Doctor then suggested that the King try exile instead. (PROSE: The Death List)

Behind the scenes

 * The gender of this incarnation was not specified in the poem; Russell T Davies chose to illustrate her as female. The numbers 1 and 3 were hidden in the swirl of her cloak.