Nephew is an Ood who lived with Auntie and Uncle on an asteroid - actually an accretion to a sentient lifeform called House.
Like Auntie, Uncle, and Idris, Nephew was brought to House throught a rift in space-time. When he arrived, he was broken, but House fixed him. There he lived with Auntie, Uncle and Idris. He tended to Auntie's and Uncle's worries in the manner of an enslaved Ood.