A city man is scheduled to be sentenced next week for having sex with his mentally disabled sister.

The 23-year-old man, who is not being named to protect the identity of the victim, allegedly had vaginal and oral sex with his adult sister inside his city apartment in February.

According to court documents, he then bathed and forced the woman to wash her mouth with soap.

When he again the following morning had sex with his sister, the woman objected, saying she knew it was wrong for a brother and sister to have sex.

The man reportedly then slapped the woman, locked his door and displayed a knife in a threatening manner, according to court documents.

However, the woman was later able to leave the apartment and seek help at a neighbor's house, according to court documents.

Court documents say personnel at Butler Memorial Hospital determined the sister had seminal fluid and a pubic hair that did not belong to her inside her vagina. She also reportedly had a bite mark on her left breast.

According to court documents, the defendant initially denied any contact with the woman. He changed his story when confronted by the hospital's findings, according to court documents.

Initially, the man was charged with rape of a mentally disabled person, involuntary deviate sexual intercourse, aggravated indecent assault, incest, terroristic threats, indecent assault, simple assault and false imprisonment.

However, as part of a plea bargain arrangement with the Butler County District Attorney's office, the man pleaded guilty to one count of felony incest.

In exchange for the plea, prosecutors will recommend a prison sentence of 11½ to 23 months when the man is sentenced Tuesday by Butler County Judge William Shaffer.