While Lucille Ball and Desi Arnaz are most often remembered as the eponymous characters they made famous on I Love Lucy, a new book is offering a closer look at their very human marriage — via their own words.

In the earliest years of their 20-year marriage, the couple — who were both in relationships with other people when they started their own romance — wrote one another letters while Desi was serving in the U.S. Army.

Those letters have since been compiled and published in a new book — Lucy & Desi: The Love Letters, out Nov. 4, 2025 — by their daughter, Lucie Arnaz.

The letters are largely written during World War II (the two married in November 1940 and Desi was drafted in 1943) and run the gamut from flirtatious to mundane. Some detail Lucy’s desperate search for a new refrigerator for her mother-in-law during the height of the war, while others show the pangs of jealousy that come with a new relationship.

In one letter, penned in 1940, Lucy writes to: “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.”

Lucie, the first child of the powerhouse duo, was born just months before the debut of their sitcom, I Love Lucy, in 1951. Speaking to PEOPLE in an exclusive interview, she said that it isn’t so much the contents of the letters that she found so surprising.

“It wasn’t unusual that there were letters that they wrote to each other, but that she kept both of them,” Lucie says. “That’s what’s so incredible to me…. And they were so beautifully kept.”

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Lucy and Desi had a well-documented tumultuous relationship, one marked by his struggles with alcohol and reported affairs. They once divorced so briefly that the breakup was invalidated by a judge. They eventually ended the relationship officially in 1960.

But the relationship has lived on for many via reruns of the iconic show, which revolved around a middle-class housewife in New York City who frequently found herself mired in schemes and hijinks as she attempted to rub shoulders with the show business types who ran in the same circles as her husband, Ricky (played by Arnaz).

So familiar was the show that, all these years later, fans often have trouble separating the characters from the actors who made them famous. Behind the scenes, the couple’s love affair was more down-to-earth — as Lucie describes in the foreword to her new book, “youthful, passionate, tempestuous, vulnerable” and “complicated.”

“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,” Lucie tells PEOPLE in an exclusive interview. “They didn’t leave each other. They were in each other’s lives forever, for always — they just weren’t married.”

Both would go on to remarry — Ball to comedian Gary Morton in 1961 and Arnaz to Edith Mack Hirsch in 1963.

Still, it was the marriage of Lucy and Desi that persisted in some strange way, Lucie says.

“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.”