Heavy menstrual bleeding is one of the most common causes of consultation in haematology. We present the clinical case of a 20-year-old woman referred by her gynaecologist due to heavy menstrual bleeding since menarche, complicated by iron deficiency anaemia. Haemostasis work-up was initially suggestive of a von Willebrand disease type 1. Genetic analyses by whole exome sequencing lead to a fortuitous discovery of haemophilia by identifying a heterozygous missense mutation in F8, exon 8 c.1127T>G:p.Val376Gly, previously reported in a patient with mild haemophilia A. The bleeding phenotype worsened by concomitant low von Willebrand factor (VWF) due to VWF variants influencing VWF levels. Our case highlights how whole exome sequencing can help to correct an erroneous diagnosis and identify polymorphisms that eventually contribute to the overall haemostatic balance.