In order to interpret irreversible microstructural processes occurring during elastic-plastic fracture of nanocrystalline materials, it is vital to elucidate multiaxial stress and strain fields in the vicinity of a progressing crack. To achieve this task, two similar freestanding notched cantilevers were fabricated by focused ion beam (FIB) milling with final dimensions of 26.5×28×125 µm3 and an initial notch depth of 9.2 µm from a nanocrystalline (nc) FeCrMnNiCo high entropy alloy (HEA). The first cantilever was deformed in situ in a scanning electron microscope using the sequential loading-unloading approach to evaluate the incremental J-integral. Additionally, a point pattern was added on the surface of one cantilever using the FIB feature milling system, allowing for the detailed analysis of the complete 2D surface strain components during the experiment. The accumulated strain around the crack tip agrees well with theoretical predictions of linear elasticity but also reveals changes upon elastic-plastic transition at the crack tip. In the crack-opening direction a butterfly-shaped tensile strain distribution is observed, reaching a maximum strain of ~65%. Additionally, cross-sectional X-ray nanodiffraction (CSnanoXRD) with a spatial resolution of 200 nm was coupled with an in situ indentation device to uncover the multi-axial stress fields associated with crack growth in the second HEA cantilever. Loads of 22, 45 and 34 mN with consecutively increasing displacement were applied, which correspond to conditions of elastic loading, crack tip blunting and void formation and coalescence, respectively. At every loadstep, the CSnanoXRD data were evaluated in a region of 30 × 35 µm2 centered around the crack tip. At a load of 22 mN, a bending stress up to ~±1 GPa was evaluated, while directly in front of the notch the crack opening stress raised to ~4 GPa, corresponding to linear-elastic fracture mechanics assumptions. At 45 mN, crack opening stresses increased to ~4.5 GPa and up to 1 µm from the crack tip a distinct plastic zone formed governed by the elastic-plastic crack tip stress field with a hardening exponent of n≈50 (Fig. 1). Further loading lead to a breakdown of the commonly assumed crack tip singularity and even lead to a significant decrease of the evaluated stress magnitude, suggesting strain softening within the nc HEA. Furthermore, the stress and strain data were used to evaluate the J-integral around the crack tip and cross-validate it with the sequential unloading approach and the J- and/or K-values computed from the stress data. It could be shown, that in materials, where plastic deformation is dominating, the sequential unloading approach overestimates the crack growth and the quantitative J-integral, the latter by a factor of ≈10, due to significant amounts of plastic deformation buildup without crack extension. The quantitative experimental strain and stress results provide unprecedented insights into the gradual stress evolution at the crack tip and across the cantilever as well as associated fracture processes in nc materials.