Jessica Simpson's upcoming memoir Open Book promises to give insight on her inner monologue and most intimate struggles, and early previews reveal that it'll contain some interesting details about her divorce from Nick Lachey.

Simpson doesn't think their separation was quite as unexpected as Lachey made it seem, and while promoting her memoir on Jimmy Kimmel Live, she let slip that she moved on from the 98 Degrees singer with a shocking, secret fling with his NSYNC rival Justin Timberlake.

Jessica Reflects On Her Marriage To Nick In New Memoir

Music fans had an emotional year in 2002, as it brought the end of Justin Timberlake's relationship with Britney Spears, but saw Jessica Simpson and Nick Lachey tie the knot and overtake them as one of Hollywood's most iconic couples.

Simpson states in Open Book that it was love at first sight when she met Lachey, writing, “In 1998, when I was 18, I met Nick Lachey of the group 98 Degrees at a Hollywood event. ‘Hi I’m Nick,’ he said. Hello, my life. I thought."

She believes that her strong faith and wide-eyed innocent approach to life made Nick reciprocate her feelings, and he proposed four years later. Unfortunately, their marriage lasted less than four years, and the couple divorced in 2006.

Related: 20 Photos Of Jessica Simpson In 2019

She Doesn't Know Why Nick Was Blindsided By Their Divorce

Lachey told the press upon his divorce from Simpson that he didn't see their split coming, but she wrote in Open Book that it was clear their relationship was suffering. In fact, they weren't even on speaking terms when she first expressed a desire to leave him.

“We had been together almost seven years when I told Nick, ‘I think I want a divorce.’ I later heard that he told the press he was blindsided. I don’t know how," she wrote. "At that point we were not even speaking to each other. Maybe he was just shocked that I stood up for myself. I don’t think he ever thought I would take the leap."

Jessica's Secret Fling With Justin Timberlake

While promoting Open Book on Jimmy Kimmel Live!, Simpson revealed that shortly after divorcing Lachey, she had a very brief fling with Justin Timberlake, whom many pop fans deemed the 98 Degrees lead singer's musical rival.

“He was out of a relationship, he was, like, over at my house. We shared a nostalgic kiss," she admitted.

Their fling didn't last very long, however, because Timberlake ruined the moment by pulling out his phone and texting someone.

"I was like, ‘Okay, I hope that’s not, like, another girl. Like, did I, like, stick my tongue out too much or, you know? But apparently him and Ryan Gosling had a bet on who would kiss me first when they were 12-years-old. And so, he texted Ryan and said he won the bet."

That was a deal-breaker for Simpson, who immediately told the NSYNC singer, "Oh, okay. Um… so we don’t kiss again. That’s done."

Next: 20 Photos Of Times Justin Timberlake Messed Up... Badly

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