Speaking to Katherine Schwarzenegger on her 'Gift of Forgiveness' podcast, Jessica explained: "I would say about eight years ago I confronted her."
"I went to her and I just said, 'I know you know what was going on and I know that you were being abused,' because she was being abused by an older guy. And basically, and he was always there at the house as well - he never touched me, but he would abuse her and then she would come to me and do the stuff to me - and so in so many ways I felt bad for her and I was allowing the abuse to happen."
"I told her in the moment, 'I know that you have a lot to deal with' and I told her that I think she should probably talk to someone and find a way to understand those moments and to forgive those moments and to heal from those moments."
"And [I said], 'I just want you to know that I forgive you and I don't really care to be around you that much or ever again, but I do want you to know that, like, I know what happened between us and I'm not gonna live in denial about it.'
Jessica was prompted to reach out to her abuser following the "soul-searching" she completed after her 2006 divorce from Nick Lachey, as she felt she "couldn't move forward" with her life without confronting her past.
She added on the podcast: "I was just in that place where I was celibate, and I was, like, on this journey to explore myself, and I knew that I couldn't move forward without letting her know that."
"I wasn't just gonna leave it unsaid. I left it unsaid for far too long, but I knew that if I was honest with her, that it would clear my conscience. And I even sent her the book and I told her that I hope it brings healing."
In her book, Jessica recalled "fiercely protecting" her sister Ashlee Simpson, from her abuser.
She wrote: "I lay between them, fiercely protecting my sister from this monster. I didn't want her to feel as disgusting as I felt โฆ I never let her near Ashlee, but I also never screamed or told her to stop."