David Tennant's return as the Doctor called for some very creative writing from Russell T Davies, but the seed for such a twist was planted years ago.
In “Planet of the Dead,” a modern era Doctor Who episode many forget about, the Tenth Doctor meets Christina de Souza.
Got a problem with that? Everything about the latest epic! See the Doctor regenerate! ...of the Tenth Doctor. Get the latest updates Christmas Trail Watch Kiss from a Rose BBC iD ...