Rihanna and Brown broke up after the incident that left the 'Umbrella' hitmaker bruised but they reunited recently despite a public backlash.
Brown, 22, says he has vowed never to hurt his girlfriend and winning Rihanna's love back took some time, the Mirror reported.
"Sometimes you row, you fight, with the one you love and things get said, stuff spirals. That night was the deepest regret of my life, the biggest mistake. But she loves me � what can I say? I'm forgiven... But, yes, I worked hard for it," Brown said.
He also dismissed Oscar host Seth Macfarlane joke on them during the Academy Awards ceremony where MacFarlane compared 'Django Unchained' as a "date night for Rihanna and Chris Brown".
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"People attack me and criticise me, it happens all the time. But they don't know me, and they don't know us. It doesn't bother me any more. Other people can judge us but they don't know anything."
I've learned a lot since that night and I've grown up. I was very young and I took a lot of stuff, fame, for granted. I didn't understand it. The support from those who do know me and the fans, who are incredible, got me through."
Rihanna recently defended brown, saying, "He's not the monster everyone thinks. He's a good person. He's giving and loving. He's fun to be around and he has a fantastic heart.