DeGeneres revisited the abuse she experienced as a teenager in an upcoming episode of David Letterman's show, "My Next Guest Needs No Introduction", reports cnn.com.
The abuse started, DeGeneres said, after her mother, Betty, was diagnosed with breast cancer.
"He told me when (my mom) was out of town that he'd felt a lump in her breast and needed to feel my breasts," she recalled in her conversation with Letterman.
"Anyway, he convinced me that he needs to feel my breasts and then he tries to do it again another time, and then another time."
DeGeneres first opened up about the abuse by her stepfather, who is deceased, in an 2005 interview with Allure.
She told Letterman she's sharing her account in the hope of empowering other women and girls.
"I'm angry at myself because, you know, I didn't, I was too weak to stand up to, I was 15 or 16," DeGeneres 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."
DeGeneres said she didn't tell her mother right away in an effort to protect her.
"I should never have protected (my mother). I should have protected myself and I didn't tell her for a few years, and then I told her," she said.
"And then she didn't believe me, and then she stayed with him for 18 more years and finally left him because he'd changed the story so many times."
( With inputs from IANS )