A South Carolina man who allegedly raped the girlfriend of his nephew on New Year's Eve was severely beaten by the nephew, police say.

William Mattson, 52, is accused of attacking the woman at a party while his nephew -- the victim's boyfriend -- was out of the house they all shared.

A mug shot of Mattson, taken after his arrest in Conway, S.C., shows a black eye, swollen lip and cuts, scrapes and bruises inflicted "by someone acting in defense (of) the victim," Conway police said.

The nephew told police he returned to the house and heard noises coming from a bedroom.

He kicked in the door to find his uncle assaulting his girlfriend, and drove the uncle from the home while administering a severe beating.

Mattson called police to report the nephew's beating of him, then returned to the house where he told arriving police officers the sexual relations with the victim had been consensual.

That caused the nephew to attack Mattson again, inflicting further injuries, police said.

The victim of the alleged sexual assault denied the incident was consensual.

Mattson has been charged with first-degree criminal sexual conduct.

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