Thinking back to your time in the Wychwood, you remember the power of the spores the A'Dendri used to enslave others. If this creature is truly Kharnus, the father of their race, perhaps the madness within the cavern would have overtaken them as well. Instead, they deceived you into coming here to slay the monster they were responsible for creating.
But their world was dying. The boundaries of their forests were being pushed ever backward by the Deepwood and they were desperate to survive. Desperate people do desperate things. Might you have done the same?