The prequel has promised to reveal the "horrifying secrets of Westeros' history to the true origin of the White Walkers", and is being run by writer and producer Jane Goldman, who is the wife of Jonathan Ross.
Bloodmoon is one of five spin-off projects being discussed by HBO, and George R.R. Martin - who wrote the A Song of Ice and Fire book series on which Game of Thrones is based - previously teased the other shows in a blog post.
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In October last year, he wrote: "Meanwhile, there are still a couple of other possible prequels in active development. I can't tell you the subject matter of those projects, no, sorry, wish I could. The readers among you might want to grab a copy of Fire & Blood when it is released on November 20, though. (sic)"
Meanwhile Naomi, 50, was revealed to have landed one of the leading roles in Bloodmoon last year.
Whilst her exact character details are being kept under wraps, it was reported she'll be playing "a charismatic socialite hiding a dark secret."
-Bang! Showbiz