Speaking at Elton John's Aids Foundation Oscars party after Sunday's Academy Awards, Brown told the U.K.'s Mirror, "Sometimes 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," he said. "But she loves me - what can I say? I'm forgiven … but, yes, I worked hard for it."
The R&B star admitted that it took many months of "serious making up" to win back Rihanna's love but he said he has grown up since that night in February 2009 when he physically attacked Rihanna, leaving her bloodied and bruised.
"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," the 23-year-old said. "I didn't understand it. The support from those who do know me and the fans, who are incredible, got me through."
Brown has blown off the public backlash against him since reuniting with Rihanna, including Seth MacFarlane's Oscar joke in which he compared the "unspeakable violence" of "Django Unchained" to a "date night for Rihanna and Chris Brown."
"People attack me and criticize me, it happens all the time," he said. "But they don't know me, and they don't know us. It doesn't bother me anymore."
He added, "Other people can judge us but they don't know anything."
Rihanna echoed Brown's comments in her own interview the Mirror published earlier this week.
"It's different now," she said. "We don't have those types of arguments anymore. We talk about [stuff]. We value each other."
She added: "He's not the monster everyone thinks. He's a good person. He has a fantastic heart. He's giving and loving. And he's fun to be around. That's what I love about him. He always makes me laugh."