Warhammer - Orion: The Vaults of Winter by Darius Hinks

At the heart the wood elf kingdom of Athel Loren, the forest-king Orion slumbers through the winter months to be reborn each spring and resume his arboreal throne. However, this year he awakens to discover a foul canker at the core of his eternal spirit – he has been cursed, though by whom and for what reason he does not know. In the grip of a furious rage he leads the asrai to war, but as the corruption spreads to the woodland realm around him, he feels his power waning and must rely upon his loyal subjects to help him unmask the traitor within their ranks.