The BBC have confirmed that the actress, Lindsay Duncan, will be appearing as Adelaide during the second Doctor Who Special. She will be playing 'the Doctor's cleverest and most strong-minded companion yet.'
"I'm thrilled to be involved in Doctor Who," said Lindsay. "I've never done anything like this before and I'm really looking forward to working with David Tennant and the Doctor Who team."
Executive Producer and writer Russell T Davies said: "Lindsay is an incredibly talented actress and I've been an admirer of her work for some time. We are delighted to announce that she will be joining the team and playing the Doctor's most strong-minded companion yet."
Lindsay Duncan has previously starred in Shooting the Past and GBH.