Does Lorick #49 bedevil you? Read it... and weep!
I'm a lady, both cunning, and fey;
Femme fatale? Yes, I curse and betray...
Stole the scabbard and sword
From my half-brother lord...
With enchantments I lead knights astray!
Hint:
My sister and nephew and me, we are biting and deadly - all three!