Oscar-winner Jennifer Hudson testified Monday that her family never wanted her sister to marry the man who’s now on trial for killing her mother, brother and nephew.

Hudson was the first witness in the Chicago trial of 30-year-old William Balfour. He faces three counts of first-degree murder for the October 2008 shootings of Darnell Donerson, 57, Jason Hudson, 29, and Julian King, 7.

Jennifer Hudson said she never liked Balfour, “not even in grammar school.” She and Balfour went to grade school together and they both grew up in the city’s Englewood neighborhood. Relatives say they didn’t like the way Balfour treated Julia Hudson.

Cook County state’s attorneys described Balfour as jealous, angry and resentful of his wife. He didn’t like her receiving gifts from family or friends. He didn’t like her young son to be affectionate toward his mother.

Prosecutors say he killed Donerson and Jason Hudson in their home on 70th and Yale on the morning of Oct. 24. According to the prosecution’s timeline, Balfour stole Jason Hudson’s SUV keys, kidnapped King and killed him in the truck. King’s body was found a few days later on the city’s West Side. The gun used in the murders was discovered not far from the residence of one of Balfour’s girlfriends.

Julia Hudson testified that Balfour told her at least 25 times, “If you leave me, you’ll be the last to die. I’ll kill your family first.”

The defense is deflecting blame for the murders on possible enemies of Jason Hudson, a drug dealer who had been previously shot. The defense team also cited the violence in the Englewood neighborhood.

“We know it’s not William,” defense attorney Amy Thompson said in opening statements. She said Chicago police were “spending time building the case [against Balfour] rather than investigating the crime.”

Thompson said DNA found on the .45 caliber murder weapon and in the stolen SUV exclude Balfour.

Julia Hudson and Balfour married in December 2006, unbeknownst to Julia’s mother and siblings. A few months later, the marriage devolved into arguments and infidelity on Balfour’s part. In February 2008, Balfour moved out of the house on Yale. Attorneys on both sides acknowledge that the couple maintained a sexual relationship during their separation.

Julia Hudson said when she suggested divorce on July 31, 2008, Balfour reiterated his threats. She said the next morning she found Jason’s .45 caliber was missing from the house.

Julia Hudson discovered the bodies of her mother and brother after she came home from work on the afternoon of Oct. 24, 2008. That morning Balfour had come by the home to talk to his wife. Julia’s birthday was the day before and when Balfour saw her celebratory balloons, he punched them and asked who gave them to her.

The couple’s divorce was finalized last week.

Jennifer and Julia Hudson separately wept on the stand as they recounted the deaths of their loved ones. Julia’s 911 tape was played for the jury as she hysterically told police her mother was dead.

Julia Hudson admitted she never called the police when Balfour threatened her.

When asked why, she answered, ‘I didn’t believe him.’