Series 12 of Doctor Who delivered some massive surprises about the Doctor's backstory. The Master finally reveals what he hinted he knew back in 'Spyfall': The Doctor is the Timeless Child, a being from another dimension who was found and taken to Gallifrey as a child, was experimented on, and became the template for Time Lord regeneration.
This revelation was seen as a way of explaining the Morbius Doctors, faces from 'The Brain Of Morbius', that many fans have suspected were previous lives of the Doctor. But with William Hartnell established as the First Doctor, and a known 12-regeneration limit, the idea of there being earlier lives of the Doctor didn't seem likely.
Although 'The Timeless Children' has delivered an explanation for how the Morbius Doctors can exist, it has raised several other new questions in the process. Will there ever be answers?
5. Why Can River Song Regenerate?
Later episodes establish that River can, in fact, regenerate. Even though she used up all of her remaining regeneration energy to save the Doctor in 'Let's Kill Hitler', she still possessed a lifespan that was far longer than the average human.
However, 'The Timeless Children' contradicts the information revealed in 'A Good Man Goes To War', saying that Time Lords gained the ability to regenerate due to gene splicing that ability from the Timeless Child into themselves. If this is the true origin of their regenerative abilities, then why could River do it without the gene splicing?