Maisie Williams, known for being Arya on Game of Thrones (and generally being amazing), is going to guest star in Season 9 of Doctor Who!
In a press release from BBC One, Steven Moffat says,
We’re thrilled to have Maisie Williams joining us on Doctor Who. It’s not possible to say too much about who or what she’s playing, but she is going to challenge the Doctor in very unexpected ways. This time he might just be out of his depth, and we know Maisie is going to give him exactly the right sort of hell.
We love Maisie and couldn't be more excited to see her wit and sass in the mix with Peter Capaldi's rather surly Doctor.