"It wasn't the same person that says I love you. It was not those... eyes," she told Sawyer in an exclusive interview. "He had ... no soul in his eyes. Just blank. ...He was clearly blacked out. There was no person when I looked at him."
The February 2009 assault left the 21-year-old battered and bruised, and Brown was sentenced to five years of probation, community labor, and one year of domestic-violence counseling.
"All I kept thinking all the time: When is it going to stop? When it is going to stop?" she said.
After the attack, Rihanna briefly reunited with Brown, but said that she never forgave him.
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"I just said to him, 'I can't do this.' I resented him. I resented him so much. And I always put the tough face on and try to, I can do anything face, and just try to play it off. But he knew. He knew it. He kept asking me, 'You hate me, don't you? You hate me,'" she told Sawyer. "And I would lie and I would say, 'No, no. And ... I did hate him. ... Everything about him annoyed me. So finally ... I just said, we can't ... we can't do this. I cannot continue to do this."
Before the dramatic incident, the couple's seemingly fairytale relationship began as a friendship. A 16-year-old Rihanna -- with a growing empire of endorsements, fashion spreads, and a bank account in the multi-millions -- said she was attracted to 15-year-old Brown's personality, humor and charm.
"We were just friends. We always played. So it was ... a good feeling to come out of the adult lifestyle and just, when you're in your room, just be yourself," she said of their year-and-a-half-long romance. "He was definitely my first big love."
But the starlet said that the deeper they fell for one another, the darker their relationship became, bordering on an "obsession."
"To fall in love with your best friend it ... can be scary because the ... the emotions get really, they get the best of you. Like it takes over," she said. "The more in love we became, the more dangerous we became for each other, equally as dangerous."
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Rihanna recounted the details of the "ugly" night, describing how she and Brown got in a heated argument over a text message on Brown's phone.
"I caught him in a lie. And he wouldn't tell the truth ... I was being more annoyed at that point in our relationship he had to lie about something so stupid," she said. "I couldn't take that he kept lying to me. And he couldn't take that I wouldn't drop it. And ... it was ugly."
According to the police affidavit, Brown shoved Rihanna into the window of his car, while driving. He punched her several times in the eye and said, "I'm going to beat the s*** out of you when we get home." When Rihanna tried to call her assistant's phone, Brown warned, "You just did the stupidest thing ever. I'm going to kill you," and threw her phone out the window.
Rihanna confirmed the brutal account, but told Sawyer she knew Brown wouldn't act on his words. "I know he was saying it to scare me," she said.