Interest in mathematics is an important factor that contributes to improved understanding and mathematical skills. Hence, it is crucial to explore factors that contribute to interest development. This study investigated the role of aha-experiences and accompanying metacognitive feelings like positive affect, certainty, and fluency in developing mathematical interest. In this longitudinal study, we examine the role of aha-experiences in a classroom context and their impact on mathematical interest in Middle school students (N=468) aged 13-16. The students completed five questionnaires, including pre- and posttests, over eight weeks. Findings indicate that aha-experiences and their related metacognitive feelings are associated with situational interest, primarily through positive affect. Moreover, there are indications that individual interest moderates the mutual relationship between situational interest and aha-experience frequency. However, no longitudinal effect of aha-experiences or metacognitive feelings on developing individual interest was observed in our sample. The findings contribute to understanding the relationship between mathematical interest, aha-experiences, and metacognitive feelings.