In recent years, a growing interest has been shown for hybrid RANS-LES approaches and their application to high-fidelity simulations of massively separated flows. Such modelling approach is intended as a way to go beyond the known limitations of the RANS in simulating massively separated flows and the computational cost of LES, which is nowadays still too demanding for a practical use. The aim of this work is to show recent advancements of the eXtra-Large Eddy Simulation (X-LES) model [1] in the discontinuous Galerkin (DG) solver named MIGALE [2]. The main features of the X-LES formulation are: (i) a clearly defined subgrid-scale (SGS) model based on the k-equation, (ii) a single turbulent kinetic energy equation switching dynamically between the RANS and LES formulations, (iii) the independence of the model from the wall distance. The LES formulation of the X-LES method has been validated and recalibrated using the decay of homogeneous and isotropic turbulence (DHIT). The sensitivity of the energy spectrum to X-LES model constants and mesh size has been evaluated. The X-LES prediction capabilities have been demonstrated in the computation of external aerodynamic problems with massively separated flows, i.e. the flow around a circular cylinder at Re = 105 and the shock wave/boundary layer interaction on a swept bump.