"[O.J. and Nicole] were two of the best friends I ever had in my entire life," Jenner tells PEOPLE in this week's issue. She is speaking out ahead of the release of the FX series American Crime Story: The People v. O.J. Simpson, which details the infamous murder trial.
But Nicole's close pal Jenner, who spoke to actor David Schwimmer as he prepared to play her late ex-husband Robert Kardashian (an attorney on O.J.'s defense team), says that though the series opens old emotional wounds, "this is going to introduce a new generation to this thing that took place that was so horrific. It could have been prevented."
Kris met O.J. and Nicole through Kardashian when she was just 17 years old.
"I went to bed one night and I woke up the next morning and my entire universe had changed," she says. "They were two of the best friends I ever had in my entire life. They were my family. O.J. was like my big brother. So I not only mourned the loss of Nicole, but I mourned the loss of O.J. and that relationship."
Indeed, the two families were incredibly close. For nearly two decades the Kardashian-Simpson clans shared vacations with their children, celebrated countless birthdays and supported each other through good times and bad. (Tragically, Jenner and Nicole even had plans for lunch the day that Nicole's body was found).
"I have these vivid memories of an amazing friendship and a life that we all had together," says Jenner, 60, adding that it was Nicole who inspired her love of interior design. "She was funny, she was beautiful and loyal and passionate and the best mom I had ever met."
Sadly, Nicole was hiding a painful secret, one that Jenner only learned of during the trial.
"I saw all the pictures and the police reports and I heard tapes of Nicole calling 911 [after she was abused by O.J.]," says Jenner.
"That was stuff I didn't know anything about. I beat myself up because I felt like I wasn't paying attention. Like, how did I miss this? But that's typical in an abusive relationship – that the woman doesn't speak out about how she's being treated."
For more from those closest to Nicole Brown Simpson and Ron Goldman on their lives, deaths and the trial that shocked the nation, pick up this week's issue of PEOPLE on newsstands Friday.
Jenner adds: "My heart breaks because of all the pain and suffering she went through. I wish I had noticed the signs. She was fighting for her life many days I'm sure. I try to pay attention to things more now. I follow my intuition."
Jenner says she hopes that the attention from FX's upcoming series, American Crime Story: The People v. O.J. Simpson will shed some light on a very real – and very widespread – issue.
"Domestic violence is a real tragedy in our lives," says Jenner. "[Nicole's death] could have been prevented. I have five daughters so of course I want women everywhere, especially women of this new generation, to know the story. They need to realize that they have a voice and they need to tell somebody if someone has hurt them. And if Nicole's legacy can be protecting other women, then that would be a really positive thing."
American Crime Story premieres Feb. 2 on FX.