"It wasn't the same person that says I love you. It was not those ... eyes," the singer, 21, says. "He had no soul in his eyes. Just blank... He was clearly blacked out. There was no person when I looked at him."
Rihanna says Brown, 20, put her in a headlock twice and bit her on the ear and fingers on Feb. 8, the night before the Grammys, in L.A. Brown was sentenced to five years of probation, six months of community service and one year of domestic violence counseling for his actions.
Despite Brown's public apology to his ex-girlfriend -- via an Internet video -- last July, Rihanna tells Sawyer she never really forgave him.
"I just said to him, 'I can't do this.' I resented him," she says. "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."
She admits that she lied to him after the February incident, claiming she didn't hate him. "He kept asking me, 'You hate me, don't you?'" Rihanna says. "And I would lie and I would say, 'No, no.' And... I did hate him. Everything about him annoyed me."
Of the pair's brief reunion in Miami nearly three weeks after the attack, the singer says she was blinded by love -- and admits she made a mistake.
"I went through a host of emotions," she tells Sawyer. "It was confusing for me. I was still attached by love. But I wasn't thinking about the reality of the situation."
Why speak out publicly now, two weeks before the Nov. 23 release of her third album, Rated R?
"I knew I had to do this in order to move on for me and in order for my fans to move on with me because it would always be a question in their mind," Rihanna tells ABC. "I don't want that five years from now every time they see Rihanna, they think of Chris Brown beating me. That's not who I am. It's just one thing that happened to me."