Reports from filming of the Peter Capaldi’s premiere episode of Doctor Who reveals that we have not heard the last of the previous Doctor Matt Smith.
In a scene that was filmed and can be seen in the below behind the scenes video, Clara receives a phone call from the past, specifically from Matt Smith’s Doctor just prior to his regeneration, during the time period we don’t see of him, inside the TARDIS, after his regeneration begins in the clock tower.
Not only does the Doctor have a final word with his companion to reassure her, he also has a short conversation with his newest incarnation:
Clara: What do you mean.. “it’s the Doctor?”
11th Doctor: I’m phoning you from Trenzalore.
Clara: I don’t understand.
11th Doctor: From the past. From before I changed. It’s all still to happen for me. It’s coming though, not long now, I can feel it.
Clara: But.. why would you do this?
……
11th Doctor: I know you’re scared, but he will be too; and he’ll need you.”
At some point the Doctor gets the phone from Clara
The 12th Doctor: So who is it?
The 11th and 12th Doctors at the same time: Oh, is that the Doctor?
