Using pp collision data corresponding to an integrated luminosity of 5.4 fb−1 collected with the LHCb detector at a center-of-mass energy of 13 TeV, the B0 → D−DþKþπ− decay is studied. A new excited Dþ s meson is observed decaying into the DþKþπ− final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be mR ¼ 2591 6 7 MeV, ΓR ¼ 89 16 12 MeV, and JP ¼ 0−, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as Ds0ð2590Þþ, is a strong candidate to be the Dsð21 S0Þþ state, the radial excitation of the pseudoscalar ground-state Dþ s meson
