However, the Master revealed to the court that the Valeyard was in fact the Doctor, or a projection of his dark side, from somewhere between his twelfth and final regeneration.

With the trial now wrecked, the Valeyard took refuge in the fantasy world he had created inside the Matrix. The Doctor discovered his plot to destroy all the high ranking Time Lords in the courtroom and defeated him. However, the Valeyard escaped, taking on a new role as Keeper of the Matrix