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. We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of e + e - pairs above the π 0 mass in the exclusive channel $dp \rightarrow npe^{+}e^{-}(p_{spect})$...