Warning Possible Spoiler for Blackwood Farm by Anne Rice

In Blackwood Farm by Anne Rice, Goblin is Quinn Blackwood's doppelganger. Goblin was his constant companion throughout his childhood. As Quinn grew and learned, so did Goblin. When Quinn was transformed against his will into a vampire, Goblin was also transformed. When Quinn was full of blood from his victim for the night, Goblin began attacking him. He made little cuts all over Quinns face and hands and filled himself with the vampiric blood. Quinn was powerless to stop the behavior.

Enter The Vampire Lestat. He tried in every way he could to help Quinn be rid of Goblin but failed even with all of his power. So he calls on Merrick Mayfair. Merrick discovers that Goblin is actually Quinn's twin who died at birth. She takes the corpse of the baby, works some witchcraft, and throws it into the flames of a pyre. Her spell worked and goblin was finally gone.