Jennifer Hudson was the first witness called Monday at the Chicago trial of her former brother-in-law, who is accused of killing three members of her family.

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William Balfour, who was married to Jennifer's sister Julia, is charged in the 2008 shooting deaths of the sisters' mother and brother and Julia's 7-year-old son.

ABC News said Jennifer Hudson, an Oscar-winning actress and Grammy Award-winning singer, tearfully testified about Julia's stormy relationship with Balfour when she took the stand at the opening of his trial.

"None of us wanted her to marry William," Jennifer said. "We did not like how he treated her."

Prosecutors said Balfour had threatened to kill Julia's family, then her, if she left him. They said Balfour was upset because Julia had a new boyfriend, even though he was seeing two other women, ABC News said.

Balfour is charged with three counts of first-degree murder. His trial is expected to last a month.