What Nicole Brown Simpson’s Family Really Knew About O.J.’s Violent Abuse Revealed in New Docuseries (Exclusive)

Nicole Brown Simpson's sisters say she spent the majority of her marriage to O.J. Simpson smiling to mask the pain of verbal and physical abuse

Nicole Brown Simpson's ex-husband, O.J. Simpson verbally and physically abused her for the majority of their seven-year marriage, yet she did what many mistreated women do: she stayed.

“I thought they were isolated incidences,” Nicole’s sister Denise Brown, 66, exclusively tells PEOPLE in this week’s issue. "The next day Nicole would be back, like, ‘Oh, everything’s okay. We talked about it. It was my fault.’”

In an upcoming Lifetime documentary series titled The Life & Murder of Nicole Brown Simpson, airing over two nights on June 1 and June 2, the Brown sisters recount an incident during a family vacation in Hawaii when O.J. assaulted Nicole after a gay restaurant patron at a neighboring table kissed their baby son Justin on the forehead.

“He was controlling but appeared generous,” sister Dominique, 59, says of her sister’s then-husband, from whom she filed for divorce in 1992. Nicole and O.J. also share daughter Sydney, now 38, and son Justin, now 35, who were upstairs sleeping at their mother’s Los Angeles home at the time of her brutal murder on June 12, 1994.

Related: How Nicole Brown Simpson's Mother Told Her Children, then 8 and 5, She Was Dead: 'Mommy’s in Heaven' (Exclusive)

“I think she thought that everything would be different having a child,” says Dominique. In reality O.J. only became more volatile. “She was pregnant, and he was calling her a fat pig,” Denise recalls.

Nicole’s other sister Tanya, 54, says she only learned the extent of O.J.’s violence during his trial for the murder of her sister and Nicole’s friend Ron Goldman. “I was looking at the pictures, and then I looked at him, and I remember saying, ‘How can you do something like this to someone you love?’ ” (The pictures of Nicole’s bruised face shown in court were taken by Denise in 1989.)

Similarly, Denise said she did not know anything about domestic violence until after Nicole's murder and then took time to learn more about it.

"That's why I think education is so important when it comes to domestic violence, the power and control of one human being over another," she says. "You need to let people know when something like this is happening. And there's so much shame involved in domestic violence, but what people have to understand is they have to be supportive."

O.J. was ultimately acquitted of the murders in the so-called “Trial of the Century.” He was later found liable in a lawsuit filed by the Brown and Goldman families in 1997 and later served jail time for separate crimes unrelated to the case. He died from cancer in April.

Related: Nicole Brown Simpson’s Sisters Break Their Silence Over O.J.’s Death: 'It’s Very Complicated' (Exclusive)

Denise says that while Nicole's murder prompted change, she is saddened that it was accompanied by tragedy.

“The Violence Against Women Act was passed due to Nicole’s murder,” she tells PEOPLE. “She is the root behind a lot of change. Unfortunately it took my sister’s life to make it happen.”

For more on the life of Nicole Brown Simpson, as shared by her three sisters, subscribe now to PEOPLE, or pick up this week's issue, on newsstands Friday.

Lifetime's upcoming project is said to explore Nicole's perspective and experience with domestic violence. The project falls under the network's Stop Violence Against Women initiative.

It will feature interviews with 50 people, including Nicole's sisters, other family members and friends, as well as never-before-seen footage of her.

If you are experiencing domestic violence, call the National Domestic Violence Hotline at 1-800-799-7233, or go to thehotline.org. All calls are toll-free and confidential. The hotline is available 24/7 in more than 170 languages.

The Life & Murder of Nicole Brown Simpson airs over two nights on June 1 and June 2 on Lifetime.

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