After 826 episodes and countless spin-off books and audio-plays (go on, try and count 'em - we dare you!), it's no surprise that Doctor Who's series continuity is as big and complex and confusing as the inside of the TARDIS.

Some fans, though, have sought to weave an even more intricate web – suggesting new twists that change the way you'll see the Doctor and his foes forever.

Paul McGann's Eighth Doctor once quipped: "I love humans – always seeing patterns in things that aren't there."

But while there's a chance we're just suffering from withdrawal, some of these theories do make a lot of sense...

1. The First Doctor was not the First Doctor

BBC

This first theory has its origin in 1976 Tom Baker story 'The Brain of Morbius', in which the Fourth Doctor engages in a literal battle of wits with the titular villain.

Morbius uses a 'mind-bending' device to do battle – and as he faces off against the Doctor, past incarnations of the Time Lord appear on the machine's display.

BBC

But there's a twist. Eight faces appear on the screen preceding William Hartnell's First Doctor – which some fans have taken to be pre-Hartnell incarnations (which was indeed the intention of the production team at the time).

So was the 'first' Doctor really the original, or not? Theory no.2 might help to shed some light on that...

2. The Doctor was one of the very first Time Lords

BBC

Looking to bring the Who back to Doctor Who, '80s script editor Andrew Cartmel devised an arc in which the Doctor would be revealed to be a reincarnation of one of the very first Time Lords, known as 'The Other'.

Hints pointing towards this reveal were dropped into a number of late '80s episodes, but the show was cancelled in 1989 before the 'Cartmel Masterplan' could come to fruition.

If you take this as fact, though, it explains away those faces in 'Morbius' – could they be incarnations of The Other?

3. The Second Doctor lived a lot longer than you thought

BBC

...or the 'Season 6b' theory.

The thinking goes that because Patrick Troughton (quite naturally) appears much older when he returns to Doctor Who for guest appearances in the 1980s, his Second Doctor must've survived his apparent demise in 1969.

Fans have devised an alternative end for this Doctor, where – rather than immediately being exiled to Earth – he undertakes secret missions for the Time Lords.

One big chunk of evidence backing up this theory is the Doctor and companion Jamie openly talking about the Time Lords in 1985 story 'The Two Doctors' – even though, in their original '60s stint, the Doctor never discussed his origins...

A continuity error? Or a hint at a huge unexplored piece of Doctor Who history? You decide!

4. The Master is the Doctor's brother (or sister)

BBC

Could the Master (now Missy) be the Doctor's brother (now sister)? That's the hypothesis put forward by some fans – and, indeed, it formed part of the early scripts for the 1996 Doctor Who TV movie starring Paul McGann.

But there's never been any confirmation of this familial link on-screen. In fact, in 2009 episode 'The End of Time - Part One', the Master refers to "my father", not "our father" – though it's possible he and the Doctor could share a mother, making them half-siblings.

Plus, the previous year's 'Smith and Jones' had the Doctor reveal that he used to have a brother, but "not anymore" – and, at this point, he believed the Master to be dead.

So... label this one a Big Fat Maybe.

5. The Daleks are unable to kill the Doctor

BBC

They screech EX-TER-MIN-ATE over and over again, but why do the Daleks never actually kill the Doctor despite having had numerous opportunities?

One theory is that they can't. The classic 1975 Tom Baker serial 'Genesis of the Daleks' saw our hero travel back in time and become involved in the terrible tinpots' very beginnings... so perhaps exterminating him would corrupt the timeline, wiping the Daleks from existence?

It's not like the Daleks to be so meditative, though – and let's not forget that they did shoot the Doctor once, almost killing him, in 2008 episode, 'The Stolen Earth'.

6. The Weeping Angels are dead Time Lords

BBC

Why do the Weeping Angels hang around graveyards and crypts so much? It's not just because they want to up their spook factor...

One scene in 2010's 'The End of Time - Part Two' has two Time Lords punished by being forced to stand stock still "as monuments to their shame" – like "the weeping angels of old."

Some fans have taken this to imply a broader connection – could the ghastly Angels be the 'ghosts' of fallen Time Time Lords?

It's one of the creepiest theories out there. To think that this might be a fate that awaits the Doctor...

7. The Doctor's Mother appears in David Tennant's swansong

BBC

Remember the mysterious unnamed character played by Claire Bloom who appeared to Wilfred Mott (Bernard Cribbins) in 'The End of Time'? (Yep, that one again!)

She was later revealed to be a Time Lord - and writer Russell T Davies has admitted he originally intended it to be the Doctor's mother... though this reveal is not explicitly featured in his final script or in the episode as televised.

Another similarly mysterious, similarly unnamed woman appears on Gallifrey in 2015's 'Hell Bent' - now played by Linda Broughton - though Steven Moffat has refused to confirm if this is the Doctor's mother, or if Broughton's character is the same as Bloom's...

8. The Doctor always regenerates into a face he's seen before

BBC

Invented by fans to explain how actors who've appeared in the show before - Colin Baker, Peter Capaldi – could later return to Doctor Who, this time as the lead.

It makes sense that the Doctor would pinch someone else's face, rather than dreaming one up from scratch – and there's evidence to support this theory, too...

When actress Mary Tamm exited Doctor Who in 1979, Time Lady companion Romana mimicked the form of alien princess Astra – with Lalla Ward, who'd played Astra, returning to the show as Romana II.

BBC

More recently, 2015 episode 'The Girl Who Died' revealed that Peter Capaldi's Doctor had regenerated into the form of Caecilius (also Capaldi) – a Roman he'd saved from the eruption of Vesuvius.

It was all a subconscious plan on the Doctor's part, y'see – a reminder that he sometimes has to bend the rules to save lives.

We've no idea why the Sixth Doctor would pick the face of brutish Gallifreyan guard Maxil (previously played by Colin Baker) though...

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