Is Maisie a young Missy? Who is the Game of Thrones actress playing in Doctor Who?

The trailer for series nine implied she was someone from the Doctor's past, but who?

The new trailer for Doctor Who season 9 was as teasing as we’ve come to expect from the show, and probably the most intriguing moment came right at the end, when Peter Capaldi’s Doctor came face to face with Maisie Williams playing an as yet unknown character. 


The Doctor certainly seems to recognise the young woman, and the ‘old man’ comment implies she is someone from the Doc’s past. But who?


It’s that time boys and girls. Let’s speculate.

What’s your theory? Tell us below!