It's a devil trying to pin down River Song's timeline – as the Doctor says, you'd need a flowchart to work it all out (which, as it happens, is exactly what we did. Handy right?).

But after the Doctor Who Christmas special and that touching encounter by the Singing Towers of Darillium, another thread of River's life has fallen into place.

Even more helpfully, now we can 'update' previous episodes with flashbacks (or flashforwards? As I say, River's a complicated woman) from other scenes in her timeline.

That's exactly what video editor Lyndon Coleman has done, taking River's 'death' scene during Forest of the Dead and adding new footage from this year's Christmas special, as well as other meetings between River and the Doctor.

It's a beautiful piece of work, and just goes to show how cleverly individual Who episodes fit into the larger whole.