Gus O'Donnell - known simply in Whitehall as GOD, is the Cabinet Secretary. In the event of a hung parliament, it is the Cabinet Secretary who has to decide the rules of engagement between the party leaders. Okay, you might say, this is mildly interesting, but it's hardly front page news. Well, true…until you add in one devilish detail…
In the event of a hung parliament, the incumbent PM has the right of first refusal to attempt to form a government, irrespective of the relative arithmetic. (There is a sound constitutional basis for this which ensures that the country always has a government in place - so a sitting PM cannot resign until a new PM in waiting has been identified.)
Politically, it's a bad break for David Cameron. And it seems his advisers have only just noticed. Back in March while they were busy planning their campaign, O'Donnell presented his plan to a parliamentary committee. That committee had Conservative MPs on it of course, but back in March they weren't expecting a hung parliament. Oops.
Of course this will never make the news at all if there is a clear or even clearish result tomorrow. But given this campaign, who would be surprised at another twist.
But there's another convention could give David Cameron the last laugh. In the event PM Cameron does emerge, it is Gordon Brown himself as the sitting PM and the monarch's principal adviser who will communicate this to the Queen. So Brown's last words as PM could be the name of David Cameron.
Catch James providing more political analysis tomorrow at 1pm in our post-election webchat.