How much did Doctor Who's The Timeless Children actually change canon?

Those in the latter camp have taken umbrage at the changes they say have been made to the Doctor's backstory and that of her race the Time Lords... but if you take a step back and really look at it, the status quo hasn't actually been altered as radically as you might think.

Allow us to break the twists of The Timeless Children down for you...

What's changed

The Doctor is no longer from Gallifrey

Now this, unquestionably, is a huge change to what we thought we knew – for over 50 years, ever since the equally game-changing story The War Games aired in 1969, we've been told that the Doctor is a native of the planet Gallifrey, home to the Time Lords. (Gallifrey wasn't actually named as such for another four years, but the basic point still stands.)

The Timeless Children establishes that in fact the Doctor originated somewhere else entirely – though where exactly is unknown.

She's found as a child on a planet far from Gallifrey, though it's implied that even this remote world is not her true home and that she actually arrived from somewhere else via the Boundary, a gateway to other parts of the universe.

So the Doctor is not Gallifreyan. That's a big deal. But it's actually the only reveal in The Timeless Children that explicitly rewrites or replaces the established mythology, as we'll see...

What's 'new'

There were incarnations before the 'first' Doctor

One of the more contentious twists in The Timeless Children is the reveal that the Doctor led many lives before she was William Hartnell's 'first' Doctor – we see the character take many different forms as the Timeless Child and it's implied that there are far more than we don't see or hear about, with the mysterious Doctor played by Jo Martin implied to be one of these in-between incarnations.

This adds to the canon but doesn't actively undo anything the series has previously treated as sacrosanct – sure, there was a reference to the 'first' Doctor being "the earliest" incarnation in 1972/73's The Three Doctors, but just three years later, Doctor Who was heavily implying that there were incarnations prior to the Hartnell version in 1976's The Brain of Morbius, so there's absolutely precedent for this twist.

The idea that Hartnell's Doctor was "the original" has always been a little sketchy, and certainly never felt as fixed as the Doctor's Gallifreyan roots.

The Doctor worked for the Time Lords' secret police

In exploring the Doctor's previously-unseen past lives, The Timeless Children also reveals that the character worked as an agent of The Division, a kind of Time Lord secret police tinkering with history. For reasons unknown, their memories of this time were erased by the Time Lords.

• Doctor Who: 13 huge questions after finale The Timeless Children

Again, this adds to canon but doesn't do away with any established 'truths' – and for anyone complaining that the Doctor's rebellious nature means they'd never willingly sign up to this sort of clandestine organisation, the character's frustration with the Time Lords' apathy and refusal to act is long-established. Would they really pass up the opportunity to step up and make a difference?

Besides, it could easily be that these experiences were what helped the young Doctor develop a disdain for military-type organisations and authority in the first place. (Sure, she doesn't remember the specifics, but these negative experiences could have made a impact on her subconscious.)

The ability to regenerate comes from the Timeless Child

We've also learnt that the Time Lords' power to regenerate was extracted from the Timeless Child, who naturally possessed the ability, and spliced into the genetic make-up of select Gallifreyans – again, this is new information but doesn't explicitly contradict anything previously established.

Bar a few passing (and often contradictory) references here and there, Doctor Who has never explicitly addressed how Gallifreyans can regenerate or what the origins of the process might be – and in fact, we've seen that regenerative energy can be passed from person-to-person (such as the Doctor and Davros in The Witch's Familiar) and that non-Gallifreyans (including River Song) can possess the ability.

Even the pre-Time Lord civilisation on Gallifrey, the Shabogans, isn't a new idea, having first been mentioned in the 1976 story The Deadly Assassin.

What stays the same

Just as important, possibly even more so, than what The Timeless Children changes or adds to canon is what it leaves intact. For all its impact, which is not inconsiderable, the vast majority of Doctor Who lore remains untouched.

The Doctor is a Time Lord

That's right – while this episode reveals that the Doctor is not Gallifreyan, it also confirms that the term "Time Lord" is simply a label that Tecteun bestowed upon himself and his elite sect with the power to regenerate. So the Doctor is still a Time Lord – in fact, she and her adoptive parent Tecteun were the very first Time Lords!

The broad strokes of Gallifrey's history

Again, though we learn much that's new about Gallifrey, very little of what's been established in previous TV stories is written out of canon by The Timeless Children.

Rassilon and Omega were still, as far as we know, the founding fathers of Time Lord civilisation (along with Tecteun, we can now presume) who discovered the ability to time-travel by converting a star into a black hole, as explained in The Three Doctors – and there's nothing that says Rassilon didn't later become the Time Lords' first Lord High President.

(Besides, these details have been fuzzy and subject to change over the years – The Three Doctors told us that Omega was Gallifrey's "greatest hero" and implied that he was the one-true founder of Time Lord society, with Rassilon not meriting so much as a mention until The Deadly Assassin three years later, so adding Tecteun to proceedings isn't even all that daring.)

The Doctor's childhood on Gallifrey – and everything that came after it

Perhaps most important of all, nothing that we understood about the Doctor's past besides her Gallifreyan roots has changed.

"I remember my home, I remember growing up, I remember you and me at the Academy together," she tells the Master upon learning of her hidden past. "That happened," he confirms. "It just wasn't your first life."

That happened. All of it. The Doctor as a child growing up on Gallifrey. Her friendship with the Master, which later turned so spectacularly sour. Stealing a TARDIS, leaving Gallifrey, and all the adventures that followed.

The Timeless Children removes none of that. And really, for all the complex and ever-shifting mythology that Doctor Who contains, it's the adventures we've watched the Doctor go on since 1963 that are the really important bit, and those are going nowhere.

• When is Doctor Who season 13 on TV?

Doctor Who series 12 is available to watch now on BBC iPlayer