Sixth Doctor's regeneration

Though the circumstances which led to the event were disputed, (PROSE: Spiral Scratch, AUDIO: The Brink of Death) the Sixth Doctor underwent his regeneration into the Seventh Doctor within the control room of his TARDIS shortly after the craft had been brought to the planet Lakertya by the First Rani. (TV: Time and the Rani) This was the sixth regeneration of the 12-regeneration life cycle beginning with the First Doctor. (TV: The Time of the Doctor)