The on-again-off-again relationship between Joan Crawford and Clark Gable reportedly lasted more than 20 years and is one of the most famous affairs in Hollywood history. Although nothing long-lasting ever came from the romance, the rumors surrounding the pair’s off-set relationship captivated audiences in the 1930s and 40s. It helped make them some of the era’s most bankable stars.

The pair made a total of eight movies together, beginning with Dance, Fools, Dance in 1931. Although the film itself was not particularly well-received, the couple’s on-screen chemistry was so good that producer Louis B Meyer demanded they instantly start work on a follow-up, and Laughing Sinners was released later the same year. (In fact, Meyer was so keen to have his two favorites back on screen together that he fired Laugh Sinners’ original lead, Johnny Mack Brown, and replaced him with Gable even after Brown had begun filming.)

But it was Gable and Crawford’s third movie together that cemented their relationship both on- and off-screen. Adapted from a Broadway play by Edgar Selwyn, Possessed told the story of a lowly factory worker who escapes her humdrum life by becoming the mistress of a wealthy attorney. Audiences were captivated with the pair’s steamy on-screen antics—and off-screen, Gable and Crawford were reportedly just as captivated with one another.

Gable and Crawford are widely believed to have fallen in love while filming Possessed. During filming, they spent many hours in each other’s company and even took weekend breaks away together despite both being married to other people. Rumors even emerged that, despite their marriages, Gable and Crawford were so in love that they contemplated eloping. In the early 1930s, however, having two of the movies’ most bankable stars embark on a steamy extramarital affair was a scandal too far, and as a result, the pair never did elope or marry. But if the rumors are true, their relationship was continued in secret for many years to come.

Perhaps for good reason, then, Gable and Crawford’s relationship during the filming of Possessed became known as the “Affair That Nearly Burned Hollywood Down.”