On the 4th the BBC snuck up a mysterious teaser video for Doctor Who. It’s called #thefourth and has voice from the 4th Doctor, as played by Tom Baker, and his companions.
Remember all the “and remember” thread running through the Clara Oswald plot? Good. This clip ends with The Doctor urging in a whisper; “Don’t you forget me.”
That said; most likely this is a teaser trailer for Mark Gatiss’ An Adventure in Space and Time docu-drama on the creation of the show.