A 74-year-old air force veteran with chronic myelomonocytic leukaemia (CMML) was referred to hematology for 9-month history of fatigue and an enlarging, painless right forearm mass. MRI revealed a 42mm subcutaneous mass. Skin biopsy showed large mononuclear cells. Bone marrow examination revealed hypercellular marrow with blasts with blue-grey cytoplasm with microvacuolation (“string of pearls”) around the periphery, with distinct tail-like protrusions (pseudopodia). Mild trilineage dysplasia was noted without expanded myeloblasts, consistent with concurrent CMML-1. Immunophenotyping showed  CD4+/CD56+variable/CD123+ clonal cells  confirming blastic plasmacytoid dendritic cell neoplasm (BPDCN). Myeloid NGS identified variants in ASXL1, NRAS, TET2, and ZRSR2. The patient started treatment with cyclophosphamide, doxorubicin, vincristine, and prednisolone (CHOP), leading to significant mass reduction after one cycle. Inactivating mutations in ZRSR2 account for nearly half of the male incidence bias in BPDCN, with 20-30% of patients having antecedent or concurrent myelodysplastic or myelodysplastic/myeloproliferative neoplasms, indicating likely common clonal origin. There can be morphological similarities between monocytoid cells in CMML and BPDCN, thereby necessitating careful correlation with clinical findings.