He affectionately called her "The Kraut," and she in return called him "Papa."
The relationship between famed American writer Ernest Hemingway and German film and singing star Marlene Dietrich spanned 30 years, and included a series of private letters that adds to the debate about the extent of their relationship.
"We are both lonelies and we ought to understand about it," Hemingway writes to Dietrich in July 1950.
ABC News has been given an exclusive look at the letters, which will be made public next week by the John F. Kennedy Library and Museum in Boston. The letters -- most of them typewritten -- were sent from Hemingway to Dietrich between 1949 and 1959.
"What do you really want to do for a life work? Break everybody's heart for a dime?" Hemingway writes from Cuba in 1950. "You could always break mine for a nickel and I'd bring the nickel."
The 30 letters, cables and even some poetry were given to the library four years ago by Maria Riva, Dietrich's only daughter, with the stipulation that they not be made public until now. They fill in the gaps of a previous collection of letters Dietrich wrote to Hemingway during that time.
"Like an incredible discovery of fossils for archaeologists, these letters are a treasure trove for Hemingway scholars. They show Hemingway both as a writer, but they also show him as a husband, as a father and a friend," says JFK Library director Tom Putnam.
The pair met on an ocean liner in 1934, and while some believe the two were lovers -- and many of the letters seem to support that -- Dietrich's family denies this and says they prove just the opposite.
"They solidify what we knew in the family … that these two people were great pals. They were buddies," says Peter Riva, 57, grandson of the late actress who died in 1992 at the age of 90.
"These two people were attracted to each other … and enjoyed talking about each other and thinking about each other when they weren't together. But there is absolutely no evidence of there being an actual affair," says Hemingway's daughter-in-law, Valerie Hemingway. "I think that it was a flirtation, and they were both very large personalities."
Yet, the correspondence expresses a longing for one another as fate intervened to keep them apart.
"I fall in love with you bad and you're always in love with some jerk," Hemingway writes in January 1950.
"Whenever he was free, she wasn't. When she was free, he wasn't. So they remained steadfast comrades right to the end," Peter Riva says.
"In a way, it's fortuitous that it didn't happen, because that might have been the beginning of the end of something," Valerie Hemingway says. Instead, Dietrich played the role of his muse.
"She was a wonderful performer, and she exuded sexuality. And Ernest just loved to be with her. But then when she was not there, she was something of a muse," she says. "He loved to write to her and think of her and talk about her in various stories."
Both Dietrich and Hemingway were known for their many romances. Hemingway at the time was on his fourth marriage. Dietrich was divorced but engaged in many high-profile relationships with actors, among others.
Dietrich told Hemingway of her affair with actor Yul Brynner, and he wrote of his chronic infidelity in one letter, saying he had a "seven-year monogamy plan" that didn't work out. She replied that she, too, had given up on her monogamy plan.