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The Fifteenth Doctor bi-generates from the Fourteenth Doctor. (TV: The Giggle [+]Loading...["The Giggle (TV story)"])

Bi-generation was a variant of regeneration which the Doctor believed to be a myth until undergoing their own bi-generation after the Fourteenth Doctor was mortally wounded by a galvanic beam in a confrontation with the Toymaker. Instead of one incarnation directly transforming into the next, bi-generation caused the new incarnation to split from the previous, allowing both to exist simultaneously; however, the new incarnation was still "older" than their previous incarnation, containing all of their predecessor's lived experiences, including those that had yet to come. During the Doctor's bi-generation, the Fifteenth Doctor was created and split off from the Fourteenth Doctor, which allowed the Fourteenth Doctor a chance to undergo rehabilitation following a lifetime's worth of trauma, while the Fifteenth Doctor continued their travels through time and space. (TV: The Giggle [+]Loading...["The Giggle (TV story)"]) The Fourteenth Doctor was not sure what lay ahead for him in the future, but wondered if one day he would fade from existence, with his future already secure in his successor. (PROSE: The Giggle [+]Loading...["The Giggle (novelisation)"])


Bi-generation internalised and built up regeneration energy that would normally be expelled. This would cause discomfort, forcing the one undergoing the process to need help being pulled in opposite directions to initiate the release; once the heads have separated, the previous incarnation and the new one momentarily shared the body like conjoined twins, with each of them having their leg and being able to pull the arm from the other's side out.

Whatever clothes worn by the one bi-generating was split between the two. In the case of the Fifteenth Doctor, he got the dress shirt, tie, underpants, socks and shoes of the Fourteenth Doctor. Unfamiliar with the process of bi-generation, the Toymaker speculated that he could repeat it by killing the Doctors again, anticipating "vast meadows of Doctors dying over and over again", but was challenged to a game by the two Doctors before he could do so. (TV: The Giggle [+]Loading...["The Giggle (TV story)"])

The ultimate fate of the preceding incarnation following bi-generation was unknown, but the Fourteenth Doctor speculated that one day he may simply fade from existence. (PROSE: The Giggle [+]Loading...["The Giggle (novelisation)"])


Main article: Fourteenth Doctor's bi-generation

While "playing" with the Toymaker, who could alter physical reality to his whims, the Fourteenth Doctor bi-generated after being mortally wounded by a galvanic beam fired through him by the Toymaker to initiate a regeneration into a new incarnation. As a result of the bi-generation, he continued to exist as an incarnation distinct from the newly created Fifteenth Doctor, who was still from his personal future. The process was assisted by Donna Noble and Melanie Bush, who each grabbed and pulled the Doctor's arms to separate the two incarnations, who both retained all their memories, and caused the garments the Doctor had on when the process occurred to separate randomly between the two of them, leaving both partially clothed.

The Fifteenth Doctor explained that he had benefitted from the time the Fourteenth Doctor would go on to spend on Earth with the Noble family, who had been "running on fumes" (TV: The Giggle [+]Loading...["The Giggle (TV story)"]) since finding out his true origins and that he was partially responsible for the Flux destroying half the universe. (TV: Wild Blue Yonder [+]Loading...["Wild Blue Yonder (TV story)"]) Remarking that they had done "rehab out of order", the Fifteenth Doctor eventually parted ways with his predecessor, having split their TARDIS in two as their prize for beating the Toymaker. The Fifteenth Doctor went on to continue their travels, while the Fourteenth Doctor took time to "slow down" and recover from his trauma. (TV: The Giggle [+]Loading...["The Giggle (TV story)"])

Behind the scenes[[edit]]

  • The Fifteenth Doctor's remark that bi-generation is "supposed to be a myth" implies the phenomenon was made possible due to the Toymaker's presence. Indeed, the Fifteenth Doctor realises he can similarly duplicate the TARDIS thanks to the lingering effect of "the Toymaker's domain", also described as "a state of play"; the Fifteenth Doctor's TARDIS explanation notably leads directly from a discussion of bi-generation.
  • In the in-vision commentary and ODWP episode for The Giggle, Russell T Davies revealed his personal theory that the bi-generation affected the Doctor's whole timeline, meaning that previous incarnations would continue to exist beyond their on-screen regenerations, mirroring the audio drama series The Nest Cottage Chronicles by Paul Magrs, which was originally intended to depict a retired Fourth Doctor after his regeneration.
  • An article speculated that the Fourth Doctor who Leela reunited with in The Final Battle [+]Loading...["The Final Battle (webcast)"] had bi-generated.[1]