What is the relationship between Arthur and Nimueh?

Arthur Pendragon was born in Camelot to Uther Pendragon and Igraine de Bois. Igraine was barren, and Uther asked the soreceress Nimueh to use her magic so that she would conceive the son he so desperately wanted. However in order for one life to be given another must be taken and as a result Arthur's mother died in childbirth.

Nimueh made it possible for Uther to have a son by magic. Igraine was barren and Nimueh used magic for her to be pregnant. However, the price to pay was Igraine to die during childbirth. In the magic of the old religion, the balance of life and death had to be restored. The life of Arthur meant the death of Igraine