'Doctor Who': Who Is Billie Piper Really Playing?

WARNING! SPOILERS for Doctor Who 15x08/2x08, 'The Reality War'.

As many fans predicted, Doctor Who's season finale, 'The Reality War', went out with a bang. While NuWho has always usually announced the departure of a Doctor, and their successor, before their exit episode airs, 'The Reality War' pulled off the revival's first surprise Regeneration, as Ncuti Gatwa's Fifteenth Doctor willingly brought on his Regeneration in order to shift reality enough to restore the existence of Poppy, his daughter with companion Belinda Chandra in the 'Wish World' alternate reality.

But perhaps a bigger surprise than the Regeneration itself was who the Fifteenth Doctor regenerated into, as the regeneration energy cleared to reveal actress Billie Piper. Piper is of course a very familiar face to Whovians, having played NuWho's first companion, Rose Tyler, when the series premiered back in 2005. Piper also portrayed The Moment, the interface of a senient weapon using Rose Tyler's face to help connect with The Doctor, in 2013's Doctor Who 5oth anniversary special, 'The Day of The Doctor'.

Despite appearances, some fans are questioning whether Piper is actually playing the next Doctor. Following a new Doctor's first appearance, the show will usually feature a credit 'Introducing.. as The Doctor'. The credits for 'The Reality War' only read 'Introducing Billie Piper'. This, coupled with Piper's own description of her role as 'One More Time', has resulted in theories of a possible twist.

So, who is Billie Piper actually playing?

A 'Fill-in' Sixteenth Doctor

At the time of filming The Thirteenth Doctor’s regeneration in ‘Power of The Doctor’, eventual Fifteenth Doctor actor Ncuti Gatwa was still busy working on Sex Education. On top of this, the next Doctor Who content scheduled at the time was for the franchise’s 60th anniversary, and it was decided that taking the lead on such a milestone could be too much pressure on a new actor just finding their feet in the role.

For this reason, the decision was made to for David Tennant, who had previously played the Tenth Doctor, to fill in, starring in three anniversary specials as The Fourteenth Doctor, a similar but slightly different incarnation. Towards the end of the the third special, 'The Giggle', The Doctor bi-generates, leaving The Fifteenth Doctor to travel the universe while Fourteen settles down to a more quiet life with Donna Noble and her family.

Currently, Disney has not decided whether to renew their co-production/streaming deal with the BBC, but it is believed to cover upcoming spin-off The War Between Land and Sea and possibly one more special, either for Christmas or NuWho's 20th anniversary. The BBC may not want to cast a new official/permanent next Doctor until the show's future is on more solid ground, so some fans speculate that Piper, similar to Tennant as Fourteen, may be acting as a stand-in Doctor for the next special.

Bad Wolf/The Heart of the Tardis

In the Doctor Who revival's season one finale, 'The Parting of the Ways', Rose Tyler, desperate to save The Doctor from a Dalek army, gazes directly into the heart of the Tardis, absorbing a large amount of energy from it. While carrying this energy, Rose briefly adopts a new identity known as Bad Wolf. Unfortunately, it is too much for a human body to sustain, so The Ninth Doctor takes the energy from Rose in order to save her life, triggering his regeneration into the Tenth Doctor.

To shift reality and ensure Poppy's existence in 'The Reality War', The Fifteenth Doctor directs his Regeneration energy towards the Tardis console, from which Rose's Bad Wolf identity had emerged. Some fans believe that this may have caused the Heart of The Tardis to manifest in corporeal form, and that Piper is playing a character somewhere between Bad Wolf and Idris, the human identity of the Tardis seen in the episode 'The Doctor's Wife'.

Bad Wolf/The Tardis is there to aid The Doctor in some way before true regeneration takes place.. some eagle-eyed fans believe they can still see Fifteen behind Piper's character following the 'Regeneration'.

The Moment

As mentioned earlier, Billie Piper also portrayed the interface of The Moment, a weapon with a conscience with which the War Doctor initially intends to end The Time War in 'The Day of The Doctor'. Much of The War Doctor's subsrquent adventure with the Tenth and Eleventh Doctors is subtly engineered by The Moment to help The War Doctor make his final decision. What actually happens is that Ten and Eleven instead opt to help The War Doctor alter history.

What happens to The Moment following 'Day of The Doctor' has never been officially explored, although it did once appear in a Titan Comics Doctor Who storyline, preventing the death of Tenth Doctor companion Gabby Gonzalez by prompting the Twelfth Doctor to intervene.

Some Whovians believe The Moment is somewhere on board The Tardis, and it's interface has emerged to guide The Doctor through a new moral dilemma.

Rose Tyler

Of course, most Whovians best remember Piper for her portrayal of companion Rose Tyler in series one and two of NuWho. Rose is trapped in a parrallell universe at the end of series two, but returns in a guest role throughout series four, trying to reach The Tenth Doctor before Davros and The Daleks trigger a Reality Bomb. Rose is ultimately returned to Pete's World, where she can live with The Doctor's human Metacrisis, who shares all the memories and feelings of The Doctor with whom she had travelled.

A theory has emerged that The Doctor’s altering reality may have caused Rose to slip from Pete’s world back into the series main reality. The actual new Doctor, or a still mid-regeneration Fifteen, will then have to help Rose get home. In the Titan Comics series, Rose and the Metacrisis Doctor have a daughter, Mia Tyler, which could add to her desire to return to the parallel world.

If whatever upcoming new Doctor Who content is marketed as a NuWho anniversary celebration, a return appearance from the original NuWho companion would seem a fitting choice. Adding to this theory is the caption on an Instagram post from Billie Piper shortly after ‘The Reality War’ aired:

“A rose is a rose is a rose!!”

Billie Piper is playing the actual Sixteenth Doctor

Finally, as unlikely as it might seem, it is not outside the realm of possibility that Billie Piper is actually our next Doctor. While actors in guest roles have, on occasion returned to play The Doctor or a companion (Peter Capaldi, Karen Gillan, and most recently Varada Sethu), Piper's return would mark the first time in the show's history that a former Companion actor has been cast as an incarnation of The Doctor.

It would admttedly be an even more difficult transition than usual, the main problem likely being convincing the audience to see Piper as The Doctor, rather than Rose Tyler cosplaying as The Doctor.

Having said that, the diversity of Piper's post-Who career proves that given enough time, she may just have the chops to pull it off.

We'll just have to wait until Doctor Who returns, whenever that may be, to find out the truth.