11 Aug 2012 02:48 PM EST

-by Vania Andre, Staff Writer; Image: Rihanna and Oprah (Image Source: Harpo Productions, Inc.)

Oprah Winfrey wasted no time asking Rihanna about her relationship with former boyfriend Chris Brown while interviewing the singer for her OWN show, Oprah’s Next Chapter.

When the 58-year-old TV mogul asked Rihanna, 24, about Brown, the singer teared up and said, “I lost my best friend.”

“It was embarrassing. It was humiliating,” she said about the assault charges Brown pleaded guilty to in 2009 after attacking her.

“I was resentful. I held a grudge,” she added. “I was dark.”

Since then the two have reconciled and even appeared on tracks together. It was rumored in 2011 they were seeing each other again secretly.

“I thought she would have been kind of a bad-ass kind of a rocker hard-edge woman—nothing could have been farther from the truth,” Winfrey said about Rihanna. “She was thoughtful. She was very emotional. She was vulnerable. She pushes the edge—she pushes the edge a lot, and there’s a reason for that.”

Oprah’s Next Chapter airs Sunday, August 19 at 9 p.m. ET on OWN.