Ellen DeGeneres is opening up about details of being sexually assaulted as a teenager by "a very bad man" who married her mother.

The talk show host first revealed the traumatic experience last year but held back specifics until speaking with David Letterman for an episode of his Netflix show, "My Next Guest Needs No Introduction," which will be released Friday.

DeGeneres said the abuse started after her mother was diagnosed with breast cancer and had a mastectomy. Her stepfather at the time used the information to sexually assault her.

"He told me when she was out of town that he'd felt a lump in her breast and needed to feel my breasts," she told 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, who said she was 15 or 16 at the time, initially kept the assaults hidden from her mother.

"I should never have protected her. 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."

Despite the trauma, DeGeneres, 61, continued to care for her mother over the years.

"I didn't really let it get to me. Until recently, I kind of went, 'I wish I would have been better taken care of. I wish she would have believed me.' And she's apologetic, but, you know," she said.

NBC News reached out to DeGeneres' mother, Betty DeGeneres but has not received a comment back.

DeGeneres previously shared part of her story during an episode of her show that aired last October, shortly after university professor Christine Blasey Ford testified before the Senate about sexual assault allegations against Supreme Court Justice Brett Kavanaugh, then a nominee going through the confirmation process.

During the show, Busy Philipps said she had recently spoken about being raped at 14 because she was inspired by Ford's testimony.

"I was so moved by her bravery," Philipps said.

A few days later, DeGeneres spoke with TODAY's Savannah Guthrie about her own assault, saying she hoped her story would help other sexual assault survivors come forward.

"As a victim of sexual abuse, I am furious at people who don't believe it and who say, 'How do you not remember exactly what day it was?'" she said. "You don't remember those things. What you remember is what happened to you, where you were and how you feel. That's what you remember."

DeGeneres declined to go into details at the time, but revealed she was a teenager at the time.

"We are really vulnerable at that age and we trust and then when you are violated, you don't know what to do and you don't want to say anything because first of all, you just start wondering, 'How did this happen, how was I that stupid?'" she said. "All of these things you think you could have controlled and you can't."