We present a computational investigation of the triplet excited states of a Rhenium complex electronically coupled with a tryptophan side chain and bound to an azurin protein. In particular, using high-level molecular modelling, we evidence how the electronic properties of the excited state manifolds strongly depend on the coupling with the environment. Indeed, only when explicitly taking into account the protein environment, two stable triplet states of metal-to-ligand charge transfer or charge separated nature can be recovered. Their interconversion gives rise to a ns time scale electron-transfer process observed experimentally. In addition, we also demonstrate how the Re complex plus tryptophan system in a water environment, experiences a too high flexibility preventing the two chromophores to be electronically coupled. This occurrence disables the formation of a charge-separated state, rationalizing the experimental observation. Our successful strategy requires a multiscale approach combining molecular dynamics and quantum chemistry. In this context, we also present the strategy used to parameterize the force fields for the electronic triplet states of the metal complex.