We report a unique case of high‐grade B‐cell lymphoma, not otherwise specified in a 5‐year‐old child. Whole‐genome sequencing revealed a DDX3X::MLLT10 fusion, usually seen in T‐cell acute lymphoblastic leukaemia (ALL). This suggests the novel idea that MLLT10 fusions are capable of driving B‐cell malignancies. An IGH deletion usually only seen in adults was also found. These unique genetic findings provide novel insights into B‐cell lymphomagenesis. The child remains in remission 7 year post chemotherapy, which demonstrates that novel complex molecular findings do not always denote high‐risk disease.