Despite their belief of such a thing being a myth, the Fourteenth Doctor underwent a bi-generation, in which he was split into two versions; himself and the Fifteenth Doctor.
The Doctor's previous regeneration, going from the Thirteenth Doctor to the Fourteenth, had been only about 15 hours earlier. (PROSE: The Giggle [+]James Goss, adapted from The Giggle (Russell T Davies), 60th Anniversary Novels (Target Books, 2023).)
History[]
A day to come[]
When Time "reunified" the Thirteenth Doctor into a singular body after she had been split into three, Time taunted the Doctor by asking "for how long" she would remain "unified". (TV: The Vanquishers [+]Chris Chibnall, Doctor Who series 13 (BBC One and BBC America, 2021).)
Cause[]
Whilst confronting the Toymaker, the Fourteenth Doctor challenged him to a game, the third they had played overall. However, as both of their games up to that point had been played by different incarnations, the first game by the First Doctor, and their second by the Fourteenth Doctor, the Toymaker declared that the next game must be played by the next Doctor and shot him through the chest with a Galvanic Beam, causing him to regenerate.
Two Doctors[]
However, instead of changing his appearance as usual, the Fourteenth Doctor recognised that something was different and asked Donna Noble and Melanie Bush to pull on his arms, causing him to begin to separate into two distinct incarnations, to the confusion of all present. The two Doctors greeted each other excitedly before pushing against each other to complete their separation.
Aftermath[]
Now separated, both Doctors challenged the Toymaker to their final game, which they won, with the Fourteenth Doctor banishing the Toymaker from existence as his reward. With a prize mallet in hand, the Fifteenth Doctor bi-generated their TARDIS as well so that he could continue adventuring while the Fourteenth Doctor could retire to heal from lifetimes of loss and battle until the time he was ready to undergo a full regeneration. (TV: The Giggle [+]Russell T Davies, Doctor Who 2023 specials (BBC One, 2023).)
Behind the scenes[]
Prior to the airing of The Giggle, the images of both the newly bigenerated Fifteenth Doctor, first seen in the trailer following The Power of the Doctor [+]Chris Chibnall, Doctor Who Centenary Special 2022 (BBC One, 2022)., and the Fourteenth Doctor preparing to "regenerate", as seen in the trailer following Wild Blue Yonder [+]Russell T Davies, Doctor Who 2023 specials (BBC One, 2023)., were modified to remove the appearance of UNIT HQ.