The new HBO boss isn't yet sold on the 'Game of Thrones' prequel series plans

The new boss of HBO has revealed that he’s not 100 percent sold on the planned Game of Thrones prequel and spin-offs.

The US network, which will wind up the fantasy after its eighth season airs in May this year, is plotting further extensions of writer George R.R. Martin’s storyworld.

X-Men and Kingsman writer Jane Goldman is working on a pilot episode based in the mythical Age of Heroes, likely to be called The Long Night, set thousands of years before the current fight for the Iron Throne.

Read more: Game of Thrones season eight – everything we know

But there has been talk of other spin-off projects too, which is where Bob Greenblatt, the new chairman of Warner Media, which oversees HBO, isn’t so sure.

“I think to figure out a way to sustain Game of Thrones or the Game of Thrones world for the future is a really good idea – if it makes sense creatively and if everybody is on board,” he told The Wrap.

“The last thing you want to do is roll out a spinoff or two and they’re not up to the standard of the original show and then you’ve just sort of failed miserably.

Read more: ‘Funniest sequence yet’ for GoT season eight

“But sure, it makes sense to try to sustain it if we can. You know, can you really do two spinoffs? I don’t know.

“I mean, I’m not even sure you can do one. You know, so I don’t know yet is the big, long boring answer and I wish I did.”

Well, one is already very much in the pipeline, filming soon in Ireland with Naomi Watts among those cast.

Game of Thrones series eight, meanwhile, will air its six extended episodes from April 14.