"The great war is between death and life, ice and fire. If we lose, the night will never end," the voiceover says.
Though it does sound like Melisandra (prone to enigmatic riddles about opposing forces), most fans seem to think the voice belongs to Laura Pradelska, who plays Quaithe, the masked Asshai priestess from the Shadow Lands. Others think the devout R'hllor worshipper, Selyse Baratheon, played by Tara Fitzgerald, set to make her first appearance next season.
HBO has given little away in their promotional materials so far. Here's season three's teaster poster, released earlier this month: