It’s a common thing for fans to decide plot and character details outwith what was explicitly stated, but far more unusual is for the writer of the work to form their own unofficial headcanon of what they’ve created. However, former Doctor Who showrunner Steven Moffat has done just that, suggesting a pair of previous episodes featured a future incarnation of the Doctor that nobody picked up on.
Back in 2008, Steven Moffat was one of Doctor Who’s most celebrated writers rather than one of its most divisive showrunners, and after the beloved “Blink,” he wrote a similarly acclaimed two-part story consisting of “Silence in the Library” and “Forest of the Dead,” featuring the first appearance of the Doctor’s future/past wife River Song.
The main crux of the story involved the Tenth Doctor and Donna exploring a library so vast it covers an entire planet and battling the Vashta Nerada, microscopic creatures that in large enough swarms appear as shadows, can devour flesh to the bone in seconds and form a rudimentary hive mind capable of communication. Interspersing the action are scenes of a little girl aware of the events and talking to her psychiatrist Dr. Moon, played by Colin Salmon. It transpires that her world is a virtual reality construct into which the consciousnesses of the dying can be saved, and Dr. Moon is an AI avatar of the planet’s artificial moon that maintains the Library’s systems. If you believe Moffat, he’s also the very final face the Doctor ever wears.
The theory was revealed in a conversation published in Doctor Who Magazine between Moffat and Russell T. Davies, the then-showrunner who it was announced a few days prior to the episode airing that Moffat would replace.
“In my head (and ONLY in my head, this will probably never appear on screen, or be confirmed in any way) River’s not just his wife – she’s his widow. Somewhere in the terrible future, on a battlefield, the 45th Doctor dies in her arms and makes her the same promise she once made him – it’s not over for you, you’ll see me again. So, River buries her husband and off she goes to have lots of adventures with his younger selves and confuse the hell out of them. But when River Song ends up on the data core of the Library Planet, she realizes she’ll never see him again. And then she starts to wonder why anyone would call a moon ‘Doctor.’ Some version of that could still work. The Doctor worrying that she’ll get lonely in the library, and popping his dying mind inside a moon.”
Despite the darker edge to many of Moffat’s Doctor Who stories, they have a tendency to feature the ultimate survival in one way or another of as many characters as possible, and he clearly wants to believe that after out-of-sync lives and subjective centuries apart, even in death his two lovers will eventually be reunited.