The television host and comedian, 61, discussed the abuse she suffered during her teenage years from her mother Betty's then-husband, who she does not name, on an upcoming episode of season 2 of "My Next Guest Needs No Introduction with David Letterman."
The comedian, who has previously opened up about being molested by the man, said she is discussing it again, "because there’s so many young girls and it doesn’t matter how old you are."
DeGeneres shared that when she was a teen, Betty's then-husband molested her under the guise of giving her breast examinations to check for lumps, after her mother was diagnosed with breast cancer.
Calling him a "very bad man," DeGeneres explained, "he told me when she was out of town that he’d felt a lump in her breast and needed to feel my breasts because he didn’t want to upset her, but he needed to feel mine."
"He convinced me that he needs to feel my breasts, and then he tries to do it again another time, and then another time," she continued.
She said that she once fled her home by escaping out a window to protect herself from him.
"He tries to break my door down, and I kicked the window out and ran 'cause I knew it was going to go more to something," she said on the episode. "I didn’t want to tell my mother because I was protecting her and I knew that that would ruin her happiness -- and she was happy with him even though he was a horrible man."
DeGeneres said she told her mother about the abuse a few years later, and her mother didn't believe her. Betty stayed with the man for 18 more years before leaving him.
"I should never have protected her, I should have protected myself," DeGeneres told Letterman. She has since reconciled with her mother.
The comedian said she doesn't want other women to be afraid to speak up.
"I’m angry at myself because, you know, I didn’t, I was too weak to stand up to [him], I was 15 or 16," she said. "It’s a really horrible, horrible story, and the only reason I’m actually going to go into detail about it is because I want other girls to not ever let someone do that."
"There’s so many young girls, and it doesn’t matter how old you are," she added. "When I see people speaking out, especially now, it angers me when victims aren’t believed, because we just don’t make stuff up. And I like men, but there are so many men that get away with so much."
DeGeneres previously spoke about the abuse she suffered to Allure Magazine in 2005.
The comedian's full interview with David Letterman hits Netflix on Friday.