"I'm sorry, Mo'Nique. I'm sorry," Gerald Imes said today on "The Oprah Winfrey Show." "I betrayed everybody's trust. I broke that trust. I broke that bond."
Thirty-seven years later, Imes admitted for the first time to the sexual abuse of his then-7-year-old sister while they were growing up in Baltimore. He was 13 years old.
"The hardest part to me was for even to admit to her that I did something wrong. I downplayed it by saying, 'If you think I did something wrong, then I'm sorry.'...I did it, I'm not proud of it," he said.
Imes said his own problems with drugs and alcohol spurred the sexual abuse. "I started using cocaine, heroine, alcohol at the age of 11. I used these drugs to hide my own pain, to hide my own fears... The drugs allowed me and afforded me the opportunity to hurt my sister," he said.
The abuse took place at night when he thought Mo'Nique was asleep, Imes said, and continued for a year or two.
"It happened more than I wanted it to," he said. "I became a perpetrator. I abused and betrayed the trust of my own sibling -- my own sister."
Imes said he was also a victim of molestation during his youth, which sent him on a downward spiral to abuse drugs and sexually molest Mo'Nique.
"I did my own molestation in pain, guilt and shame. I thought it was my fault that these things happen. I internalized that. I hid behind drugs and alcohol," he said. "I'm not a monster. I'm her older brother."
He said he never told his sister not to come forward, and never groomed her, or lured her with candy, as his sister told Essence magazine in 2008.
Mo'Nique's representatives did not immediately respond to ABCNews.com's request for comment.
Mo'Nique, 42, opened up to Barbara Walters about the extent of her sexual abuse, which she said consisted of "touching your breast, someone rubbing your vagina, someone rubbing your behind, someone rubbing up against you with their private parts."
She told Walters that fear prevented her from telling her parents. "I think for the same reason most people don't tell. You're afraid. I was afraid of my brother," she said.
Mo'Nique said the only apology she ever got from her brother was half-hearted: "The apology that I got from my brother is, 'If you think I did something wrong, then I'm sorry.'"
Imes said he wished his sister could have addressed her pain and raised the issue privately with the family before sharing it with the world.
"I'm hurt," Imes said. "I feel like this could have been done in house, to the point that everyone wouldn't have been exposed."
Mo'Nique has said she was able to use her childhood experience when she accepted the role of a lifetime, playing the abusive mother Mary in the film "Precious: Based on the Novel Push by Sapphire."
"My brother was a monster to me," she told Essence magazine. "I became my brother" when director Lee Daniels called "action" on the set.
Her performance earned her kudos, along with an Academy Award and Golden Globe award for best supporting actress.
In her Golden Globe acceptance speech, Mo'Nique dedicated her award to victims of abuse: "I celebrate this award with all the Preciouses, with all the Marys -- I celebrate this award with every person that's ever been touched. It's now time to tell. And it's OK."