William Balfour reportedly threatened to kill Jennifer Hudson's family two months before they were killed.

Witness Robbin Myers claimed he met William at his own son's birthday party and reveals he was agitated and had a gun handle in his waistband.

He also claimed his wife Julia - Jennifer's sister - was cheating on him.

Robbin claimed William said: ''If I find that she cheating on me, I'm f**king her and him up.''

He also reportedly referred to her brother Jason as a ''fat ass'' and his wife as a ''fat bitch''.

Earlier today (26.04.12) - in what is the fourth day of testimony at the Cook County courtroom in Chicago - it was also revealed William was cheating on Julia with Diane Grant.

She revealed the night before Jennifer's mother Darnell, brother Jason and nephew Julian, were shot he did not have sex with her, which she thought was unusual.

Diane added she did not know he had a wife until two months after she met him, at which point she was in love with him and would continue to spend the night with him.

Balfour is charged with first degree murder in their deaths in addition to home invasion, aggravated kidnapping, residential burglary and possession of a stolen motor vehicle.

He has pleaded not guilty.

The trial is expected to last for approximately four weeks.