HBO’s hotly anticipated prequel to “Game of Thrones,” which will star Naomi Watts in an unknown role, is shrouded in mystery.

We know its working title is “Bloodmoon” and it’s set thousands of years before the events of the show — so no chance of character cameos except for maybe Melisandre (Carice Van Houten), since she was ancient.

But in a new interview with EW, George R.R. Martin spilled the beans about a few key details.

First, forget the seven kingdoms of Game of Thrones — this world will have a whopping 100

“We talk about the Seven Kingdoms of Westeros; there were Seven Kingdoms at the time of Aegon’s Conquest,” Martin explained “But if you go back further then there are nine kingdoms, and 12 kingdoms, and eventually you get back to where there are a hundred kingdoms — petty kingdoms — and that’s the era we’re talking about here.”

He also confirmed that ancient Starks will be part of this world, as will Direwolves and White Walkers…and mammoths. That’s right, get ready for prehistoric Westeros.

Interestingly, although there will be Starks, he said there will be no Lannisters. Their ancestral home of Casterly Rock will be occupied by the Casterlys. Martin said, “The Lannisters aren’t there yet, but Castlery Rock is certainly there…It’s actually occupied by the Casterlys — for whom it’s still named after in the time of Game of Thrones.”

In the mythology of this world, the Casterlys were eventually overtaken by Lannister ancestor Lann the Clever — classic Lannister move.

So although there’s been speculation that Watts’ character could be Lann the Clever, chances are she’s a Casterly. Perhaps the last of the Casterlys. The Lannisters send their regards.

There’s no word yet on an air date.