This poster presents a search for charged Higgs bosons decaying into 𝑊𝑊 or 𝑊𝑍 bosons, involving experimental signatures with four leptons with a variety of charge combinations, missing transverse momentum and jets. We are using a data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV measured with the ATLAS detector between 2015 and 2018. The total integrated luminosity for this data is 139 fb−1. The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged 𝐻 bosons, or the associated production of a doubly charged 𝐻 boson and a singly charged 𝐻 boson. No significant deviations from the Standard Model predictions are observed. 𝐻 bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively.