The Diamonds singer was attacked by her then-boyfriend on the night before the Grammy Awards in 2009.
Brown was convicted of assault and sentenced to probation.
He was also slapped with a restraining order to keep him away from the singer.
However, they later rekindled their relationship in 2012 and Rihanna got the order lifted.
The singer has now revealed she gave Brown a second chance because she thought he could change.
"I was that girl... that girl who felt that as much pain as this relationship is (sic), maybe some people are built stronger than others. Maybe I'm one of those people built to handle s**t like this," she tells Vanity Fair magazine.
"Maybe I'm the person who's almost the guardian angel to this person, to be there when they're not strong enough, when they're not understanding the world, when they just need someone to encourage them in a positive way and say the right thing."
When asked if she thought she could change him, she replies, "A hundred per cent. I was very protective of him. I felt that people didn't understand him. Even after (the assault)... But you know, you realise after a while that in that situation you're the enemy. You want the best for them, but if you remind them of their failures, or if you remind them of bad moments in their life, or even if you say I'm willing to put up with something, they think less of you - because they know you don't deserve what they're going to give.
"And if you put up with it, maybe you are agreeing that you (deserve) this, and that's when I finally had to say, 'Uh-oh, I was stupid thinking I was built for this.' Sometimes you just have to walk away."
Despite being linked to a string of men including Leonardo DiCaprio and racing driver Lewis Hamilton, Rihanna admits Brown, who she split from in 2013, was her last official boyfriend and she still has feelings for him although they are no longer friends.
"I don't hate him. I will care about him until the day I die. We're not friends, but it's not like we're enemies. We don't have much of a relationship now."
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