"This happened to me. ... It can happen to anyone," the singer, 21, tells Diane Sawyer in an interview airing Thursday on Good Morning America and on 20/20 on Friday.
Rihanna says it was particularly difficult because of the special place Brown held in her heart: "He was definitely my first big love."
Both singers have worked to move on. Brown is serving a community labor sentence in Virginia and working on new music for an album titled Graffiti that will drop Dec. 15. Rihanna is shaking things up with her edgy fashion and releasing her fourth album, Rated R, on Nov. 23. The album's first single "Russian Roulette" debuted last week.
PeopleTV Archive: Watch Rihanna’s Changing Look