Evidence-based interventions to favor more harmonious interactions in difficult relationships remain scarce. This study examined whether compassion training may have beneficial effects in an ongoing tense relationship with a disliked person, by reducing schadenfreude toward them and increasing felt interpersonal closeness. 108 participants were assigned to one of three 5-week trainings in a longitudinal randomized controlled study: compassion training, reappraisal training (emotion regulation control condition), or Italian language training (neutral active control condition). The disliked person was not targeted during the trainings to test potential transfer effects. Misfortune scenarios and a measure of interpersonal closeness were used to test whether schadenfreude and closeness feelings toward a disliked person changed from pre- to post-training, across different experimental and control groups. Only compassion and reappraisal trainees reported a decrease of schadenfreude feelings toward the disliked person compared to their pre-training ratings, no changes were observed in the Italian language training. Importantly, feelings of closeness toward the disliked person increased in the compassion training group compared to the other two groups. This increase of closeness feelings could be a central mechanism for improving social interactions. These transfer effects open new perspectives concerning emotion regulation interventions in conflict resolution.