The more popular any TV show or movie is, the more likely it is for many fan theories to appear. And as one of the most celebrated and longest-running science fiction series of all time, Doctor Who has gotten its fair share of fan theories over the years. Some were downright bizarre and are unlikely to be confirmed anytime soon, if ever.

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On the other hand, multiple Doctor Who fan theories turned out to be true, much to the delight of the fans who supported the theory. These successful fan theories concern various things, from the Doctor's complex relationships to the details of the regeneration and many more fascinating things.

6 The Master And The Doctor Have A Love-Hate Relationship

Missy kisses the Doctor in Doctor Who

Back when the Master first appeared in the series, some fans started to think there was a love-hate relationship between him and the Doctor. This is called shipping, and it's a common enough phenomenon in pop culture when two characters are believed to be romantically involved by the fans or at the very least attracted to each other, even if it's not substantiated by the source material.

However, Doctor Who later confirmed this theory to a certain degree. Once the Master has turned into Missy, played by Michelle Gomez, Missy did try to hurt the Doctor and his companions...but she kissed the Doctor before that, proving she didn't entirely hate him after all.

5 River Is Amy's And Rory's Daughter

River Song Screwdriver

After Amy, Rory, and River were introduced, some fans came up with the theory that River might be Amy's and Rory's time-traveling daughter. As all viewers who watched the show will know, that's exactly what happened. Amy named her daughter Melody Pond but when translated into a different language, Melody Pond changed into River Song.

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What makes this even stranger is that Amy named her daughter after a childhood friend Melody...who was a regeneration of River! So River spent their childhood with her parents even before they became her parents, which is something that would only be possible in the time-traveling world of Doctor Who.

4 The Master Isn't Dead

doctor-who-The-master

Another theory concerning the Master is that he didn't die. When the Master was supposed to have died in the older seasons, the fans questioned it and were quick to point out he could very well be back with a different face. That did happen as the Master always crossed the Doctor's path, sooner or later. One of the main reasons why killing the Master off for good wouldn't be a good idea is his popularity among the fans.

Just like Loki from the MCU, the fans love the Master, so even when it was presumed that both Loki and the Master died, they showed up repeatedly later on to once again make Thor's and the Doctor's life more complicated. Of course, the Master also has the added advantage of being able to regenerate, which makes it difficult to get rid of him for good.

Doctor Who Gwyneth

In the third episode of the first season of the renewed Doctor Who, the Ninth Doctor meets Charles Dickens...and also the girl Gwyneth played by Eve Myles. Gwyneth dies in the end but not before she helps the Doctor save the day. Eve Myles went on to play Gwen Cooper, one of the leading characters in Torchwood, so it was natural for the fans to speculate the two women were somehow related.

The final episode of the fourth season confirmed this, explaining that Gwen and Gwyneth looked alike due to spatial genetic multiplicity. A similar theory states that the Doctor takes on new faces based on people he has met in the past. And since the Tenth Doctor once met a man who looked a lot like the Twelfth Doctor, this theory also was confirmed later on.

2 The Word Doctor Owes Its Existence To The Doctor

A still from the Doctor Who episode Midnight

A fan theory suggested the word doctor was created thanks to the Doctor who was helping, "healing" those who needed it, not just on Earth but across countless worlds. What makes this theory even more interesting is that the fan who created it in 1995 was none other than Steven Moffat, a future showrunner of Doctor Who!

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Unlike other fans of the show, Moffat got the chance to build his fan theory into the show. So years later after the theory first appeared, River confirmed it and explained the origin of the word "Doctor."

1 The Doctor Can Regenerate Into A Woman

doctor who jodie whittaker

Even though the Doctor actors were predominantly male, the fans believed there was no reason why the Doctor couldn't one day regenerate into a female. The first one who did this was, of course, the Master, aka Missy, but the Doctor eventually followed as well and after Peter Capaldi's Twelfth Doctor, the Thirteenth Doctor wore Jodie Whittaker's face. This theory and the subsequent regeneration into a female throws a wrench in another popular theory - which is that the Doctor can choose their new form. Considering how surprised the Thirteenth Doctor is when she learns that she's a woman, it's more likely that the Doctor doesn't pick what he's going to look like, let alone what gender he's going to be.

Of course, in the short 1999 Doctor Who parody movie Doctor Who and the Curse of Fatal Death, the Doctor (originally played by Rowan Atkinson) regenerated into a woman, years before Peter Capaldi's Doctor did! What's more, in the movie, the Doctor and the Master seemed to have gotten together, confirming yet another longstanding Doctor Who theory years before the Twelfth Doctor era. But considering that the parody isn't a part of the official show, it's safe to say that both of these fan theories weren't confirmed until the renewed Doctor Who aired.

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