In Doctor Who, one of the Series 12 (2020) stories had that twist, and what stands this story apart from almost all other uses of this trope is that the twist w

In Doctor Who, one of the Series 12 (2020) stories had that twist, and what stands this story apart from almost all other uses of this trope is that the twist was not an ending, and we see how characters process that reveal. Please be careful if you gonna read TV tropes page linked in a sibling comment, as the title of that episode is in the list of examples on that page in Live-Action TV section, so you can accidentally spoil yourself all the fun.