The introduction of a new Doctor is, like, a pretty big deal on Doctor Who. So when season 12’s “Fugitive of the Judoon” brought us Jo Martin’s Doctor on the lam, it felt like the culmination of something huge. But it turns out her debut was kind of out-of-the-blue—and one the showrunner doesn’t know will come again…
Source: io9 – Doctor Who’s ‘Fugitive Doctor’ Was an Unplanned, Last-Minute Twist