In a new interview on Sirius XM's "Radio Andy," the 98 Degrees singer -- who was married to Simpson from 2002 to 2006 -- explained why he hasn't picked up a copy of his ex's memoir and doesn't have any plans to do so.
When Cohen asked if he's read the book, Lachey laughed and said, "You'll be shocked to hear that I have not, nor will I ever read that book."
"I mean, obviously I knew the book was coming out, but I lived the book," he added. "You know what I mean? I know what the truth is, so I don't need to read it or read someone's version of it in a story. You know, I know it. I lived it. So no, I never read it."
Cohen went on to bring up that a fictionalized docuseries based on Simpson's life is in the works, and suggested that Lachey would have some interest in how he will be portrayed and who will play him in the show. However, Lachey laughed it off, before sharing that "it's not even on [his] radar."
"I'm thrilled to be where I am in life," he explained. "I mean, that was 20 years ago. So it's honestly the last thing on my mind these days, except when someone brings it up."
"I mean, I understand why people want to ask, but it's just, it's so not a part of my life anymore," he added. "It's not even on my radar. She's doing her thing and I'm doing mine and that's the way it should be."
In Simpson's 2020 memoir, "Open Book," Simpson detailed the early days of their relationship, their marriage and subsequent divorce. She wrote that things between them really fell apart when they started shooting their reality series, "Newlyweds." She'd accuse him of having a "wandering eye," he'd blow up and disappear with his boys for a few days and not even marriage counseling was much of a help. She claimed they slept together once after separating and while it was "emotional," she said there "was no connection" anymore. "When he walked out the door, I knew I would never see him again," she wrote -- and she didn't.
Earlier this year, the book was re-released in paperback. In a previously unseen handwritten diary entry, Simpson addressed her divorce from Lachey and reacted to him moving on with his now-wife Vanessa Minnillo.
"I didn't want to be married any longer but I was also afraid to be alone with 'no one to call my own but the night,'" she wrote. "The house is hushed. Everything is still. I sit in solitude. To cry. To feel alone…."
"What a shame to find that which is or who is to blame, because in this world, deceit becomes a crippled hearts cane," she continued, before mentioning Lachey directly.
"So, Nick, you're with another already? Seems that you forgot the love you spoke to me," she continued. "I'm saddened beyond belief. Alone in the dark, with no one to call my own but the night."
She concluded her entry by adding, "Oh night, love me tenderly, love me quiet, find me happy, find me right. Oh lord, let your star shine upon me tonight."
Simpson and Lachey's divorce was finalized in 2006 and Lachey began dating Vanessa the same year. The two tied the knot in 2011 and now share three children. Simpson, meanwhile, eventually met Eric Johnson and has three kids with him as well.