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Simpson was charged with the murder of ex-wife Nicole Brown Simpson in 1994 and was acquitted of criminal charges.
Jenner, who was close friends with Brown Simpson, revealed that she was present at the trial as often as she could be, and explained to People magazine why watching her ex-husband defend Simpson was difficult.
"They were trying to save O.J. from going to jail. It was very hard," Jenner said.
Jenner, 60, also discussed the most "stressful" parts about the trial, noting that she "just wanted it to be over so that we could all try to pick up the pieces."
"It was excruciating to see how painful it was for the families to hear them go over and over all the details of what had happened," Jenner said. "It went on for so long. It was very stressful."
Jenner described the scene in the courtroom after the verdict was read and revealed that she was "numb" after hearing that Simpson was found not guilty.
"We didn't know what the verdict was going to be," Jenner said. "I couldn't breathe. When the [not guilty verdict] was read, everybody was stunned. I was just numb. And seeing the photos of [O.J. and his defense team] celebrating, it was hard."
More than 20 years after the trial, Jenner noted that Brown Simpson is still in her heart and that she will never fully get over her death.
"Losing her was something that I can never quite get over," Jenner said. "But I will always have such love in my heart for Nicole. She is a part of my life that will be there forever."