Ovarian granulosa cell tumor (GCT) is a malignant tumor with slow progression. The recurrence of granulosa cell tumor often happens after 5 years, leading to a 'forgotten tumor' by the patient. We present the case of a 64-year-old woman with a presentation of left flank pain. An initial computed tomography scan revealed a single tumor with multiple adjacent organ invasions. Surgical intervention was prescribed and the pathological results revealed a metastatic granulosa cell tumor. We also review the literature for the follow-up and further management of this tumor.