The I Love Lucy stars were married from 1940 to 1960, although their relationship was marred by busy scheduled, reported affairs and complicated feelings

Lucille Ball and Desi Arnaz had simultaneously one of the most romantic and chaotic marriages in Hollywood. While they were together for two decades, tying the knot in 1940 and remaining married until 1960, their marriage was marred by infidelity, addiction issues, complicated feelings stemming from multiple miscarriages, and the pressures that came with being the most famous couple on television. Just four years into their marriage, Lucille filed for divorce from Desi, although her claim was quickly dismissed when they reconciled not long after. And a decade into their marriage, they created and starred in I Love Lucy together.

The couple welcomed two children while together, with their oldest, daughter Lucie Arnaz, now 74, spotlighting the early years of their relationship and marriage in a new book, Lucy & Desi: The Love Letters, which includes several of the letters saved by Lucille over the years, featuring her correspondences with Desi primarily when he was away during World War II.

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“It wasn’t unusual that there were letters that they wrote to each other, but that she kept both of them,” she told People, coinciding with the book’s release on November 4. “That’s what’s so incredible to me…. And they were so beautifully kept.” However, one thing she highlighted was that the letters paint a very different picture of Lucille and Desi when you compare them to Lucy and Ricky.

From 1951-57, the couple played Lucy and Ricky Ricardo, a well-to-do young married couple living in New York City, interacting most often with their landlords Fred and Ethel Mertz. Lucy and Ricky get into several scraps over the course of the series, with the former often asking for an extravagant demand from her husband, while the latter exasperatedly admonishes her and blurts: “Lucy! You’ve got some ‘splainin’ to do!”

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Behind the scenes, and away from their characters, Lucie describes them as “youthful, passionate, tempestuous, vulnerable” but also “complicated,” highlighting some of the more tough moments in their marriage, specifically in the latter half, while their show was taking off. “Maybe the last 10 years or 8 years of the marriage were uncomfortable and very hard for them both, but after they separated, everything softened.”

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They remained in each other’s lives throughout despite separating. “They didn’t leave each other. They were in each other’s lives forever, for always — they just weren’t married.” She highlights how strong their bond was with passages from her mom’s letters like: “I think of you instantly upon waking– all day – all nite – until I go to sleep again. Maybe that’s why you sounded so kinda sad + bored with me last nite.”

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Despite finding love with others over time, Lucie saw how much her parents’ relationship still endured. “They were married to other people, but they were still a couple in a weird way, you know … they respected each other’s marriages and each other’s partners as something that made more sense, maybe — Maybe those people were better for them at this particular time in their life, but I don’t think it was ever as passionate as it was with just the two of them.”