It's understandable why people couldn't stop talking about 'Game of Thrones' actress Maisie Williams being cast in a mysterious role in the new season of 'Doctor Who.' After all, there should be a good reason why a major star would be given the role of Ashildr.

But who is Ashildr? And is there a possibility she will be staying in the show longer than just the two announced episode?

[SPOILERS AHEAD]

A new theory has emerged from TV.com stating that Maisie Williams' Ashildr is the human form of the TARDIS based on the following equation:

ASHILDR = A S I D R H L
H + L = 8 + 12 = 20 = T
ASHILDR = A S I D R T = TARDIS

The site is also quick to point out that 'Doctor Who' showrunner Steven Moffat is fond of introducing mystery characters with names that point to a previous character. Notable examples are Amy and Rory's daughter Melody Pond actually being River Song, and Missy being a nickname for "Mistress," which is the female form of "Master."

Naturally, there are several other theories that can go hand in hand with the 'Ashildr is TARDIS' theory. One fan points out that the TARDIS has previously taken a human form in the episode 'The Doctor's Wife,' where the matrix is placed in a woman named Idris. In the episode, Idris helps the Doctor escape but is killed in the process.

Interestingly, before Idris dies in 'The Doctor's Wife,' she tells the Doctor that she will not be able to speak again but will always be there for him. Did the matrix of the TARDIS somehow find a way to reach out to the Doctor again by taking another human form?

Will the identity of Maisie Williams' Ashildr finally be revealed? Find out when the new 'Doctor Who' episode 'The Woman Who Lived' airs on October 24.