What was the "rumour" Cersei mentioned in this week's Game of Thrones?

That was the enigmatic exchange between Cersei and her right-hand man Qyburn in the latest episode of Game of Thrones – but what could it mean?

Coming as it did immediately after Cersei's son King Tommen had betrayed her – giving her up to be tried for her moral crimes under the direction of the High Sparrow – you might assume the "rumour" was something from the religious leader's past that could somehow throw into question his own piety. Some moral transgressions of his own, perhaps (maybe he's secretly been a customer at Littlefinger's brothel).

But more likely it is something far, far worse than that...

The rumour in question is probably that there is still a cache of Wildfire hidden in King's Landing, and that Cersei intends to burn the place to the ground.

In case you've forgotten, Wildfire is the devastating liquid flame Tyrion reluctantly used to decimate Stannis's ships at the Battle of Blackwater.

We know Cersei lives only for her children (plus Jaime, of course) and after the murders of Joffrey and Myrcella it sounds as if the Sparrow's 'corruption' of Tommen could be about to lead her to the same extreme measures.

But what's the evidence that there is actually more Wildfire knocking about?

Well, we saw what looked very much like the deadly green flames careering down the corridors of King's Landing during Bran's extended vision in episode six. While they were only brief glimpses, when you slow the whole thing down it becomes clear just how frequent and long those sequences are compared with most of the others. It's like they want us to make the connection...

And it seems there could be "more" – "much more" – of it than Cersei and Qyburn had originally hoped.

On top of that, there have been a number of more subtle hints that something of this nature was coming. We know how George RR Martin and the Game of Thrones writers like to sneak those prophetic little suggestions in, and earlier this season Cersei told Tommen "I would do anything for you... anything to keep you from harm. I would burn cities to the ground."

Then, in the latest episode, Jaime pointed out to Edmure Tully that their sisters have much in common when it comes to how protective they are of their children: "They’d do anything to protect their babies. Start a war... burn cities to ash…"

If that's not foreshadowing, I don't know what is.

There is an irony, of course, in Jaime's beloved Cersei potentially threatening to burn King's Landing and its people with Wildfire. The last person to do that was Aerys II Targaryen, "the Mad King" – and Jaime was the unsung hero who stuck a sword in his back in order to stop him...