Game of Thrones only has 13 episodes left — so HBO is planning for the future of its most valuable property.

The network is mulling over four different potential follow-up series from various writers, according to The Hollywood Reporter. Each of the four possible spin-offs will explore a different time period in Westeros. It's a very big world George R.R. Martin has created, and there are any number of viable prequel, sequel or spin-off ideas that could be explored.

The writers/writing teams are: Max Borenstein, who's the main screenwriter for MonsterVerse film franchise and was the showrunner for Fox's short-lived Minority Report; X-Men screenwriter Jane Goldman and George R.R. Martin, who is of course the author of the A Song of Ice and Fire book series on which Game of Thrones is based; Oscar-winning screenwriter Brian Helgeland; and Mad Men and The Leftovers writer Carly Wray and Martin again.

Emilia Clarke, <em>Game of Thrones</em>Emilia Clarke, Game of Thrones

All four potential spin-offs are in early developmental stages. HBO is planning to wait until the scripts are in and then decide on how to proceed. This doesn't mean that there will be four Game of Thrones spin-offs, just that HBO is exploring a lot of different options and wants to make sure it makes the best choice for a follow-up.

Current Game of Thrones showrunners David Benioff and D.B. Weiss are not attached to write any of the new scripts, but would be executive producers on anything picked up to series. Martin would also get an executive producer on any new series.

Game of Thrones Season 7 premieres Sunday, July 16 at 9/8c on HBO.