Doctor Who’s final anniversary special, 'The Giggle', introduced the concept of 'bi-generation', and it’s thrown the whole Whoniverse into chaos. Now, we’re going to get into spoiler specifics below, so make sure you’re up to date on all things Who before going any further.
As the regeneration came around, it turned out that the Doctor could now split into two, rather than simply regenerating into a new version of themselves. This means that David Tennant’s 14th Doctor and Ncuti Gatwa’s 15th Doctor can now both exist in the Doctor Who universe.
