The credits rolled shortly after the Sixteenth Doctor's new face appeared, so we have nothing to go on as to why this happened. I do have just about a million questions, though.

The Doctor is dead. Long live the Doctor! The era of Ncuti Gatwa's Fifteenth Doctor came to a surprise end on Saturday night, as the Time Lord regenerated at the end of "Doctor Who" season 2 ...

The Doctor now having Rose Tyler's face may imply she has "unfinished business," but it wouldn't make the most sense if that business were with her former companion.