Jennifer Hudson was the surprise first witness today in the murder trial of the man accused of killing her family members.

William Balfour is in court for the slaying of Jennifer's mother Darnell Donaldson, brother Jason Hudson and seven-year-old nephew Julian King in the 2008 triple-homicide.

E! News reports that the Oscar winner was very emotional as she recalled warning her sister Julia Hudson against marrying William.

"I told her over and over again to not marry him," the Dreamgirls star said. "We did not like how he treated her."

Jennifer revealed that she last saw her family a life a week before they were killed in a surprise visit home.

"It was my mother, my brother, my sister and my dog. Thank God I had the opportunity," she said adding that she spent time playing piano with them. She then became overcome with emotion.

Lead prosecutor James McKay told the court that William threatened Julia just a day before the murders.

"If you ever leave me, I'm going to kill you, but I'm going to kill your family first," William allegedly said.

The defendant has pleaded not guilty and faces life in prison if convicted.