This report details the case of a 24-year-old Filipino individual born with ambiguous genitalia, assigned female at birth, and raised as such. Around the age of 13, the patient began to develop secondary male characteristics. Medical assessment was postponed until the onset of abdominal pain led the patient to seek consultation. Cytogenetic testing revealed a sex chromosome disorder of sexual development with a mosaic karyotype of 45,X/45,X,del(X)(q13). Imaging, surgical exploration, and histopathologic evaluation confirmed that a pelvoabdominal mass originated from the left ovary and was a mixed germ cell tumor containing yolk sac tumor and mature teratoma components. At presentation, the patient also reported symptoms consistent with gender dysphoria. This case highlights the wide phenotypic variability of mosaic Turner syndrome and reinforces the importance of accurate neonatal sex assignment in individuals with DSD. It further emphasizes the need for healthcare providers to remain vigilant for such presentations to enable prompt, tailored, and comprehensive management.