Stress partitioning among austenite, ferrite, and B2-(Ni,Fe)Al intermetallic precipitates within the ferrite phase of an aluminum-added duplex steel was studied by in-situ high-energy X-ray diffraction experiments during tensile loading at the P21.2 beamline of “Deutsches Elektronen-Synchrotron“, DESY. By analysis of 2D diffraction patterns in azimuthal angles corresponding to the tensile loading direction, diffraction data were obtained for scattering vectors near the tensile axis. By analyzing peak shifts for the \{100\}_B2 superlattice reflection and converting lattice strains to microstresses by assuming a uniaxial stress state, stress levels up to four times the macroscopic (average) stress level were confirmed in B2 precipitates. Besides, the \{100\}_B2 peak underwent splitting in the course of plastic deformation. Splitting was attributed to the bimodal size distribution of B2 precipitates, with fine and coarse B2 precipitates carrying two different stress levels. The observation of significant microstresses for \{100\}_B2 is consistent with the documented occurrence of \{hk0\}〈100〉-type glide in B2-NiAl. For the preceding glide system, loading in directions closely aligned with <100>_B2 results in near-zero Schmid factors, indicating the difficulty of yielding. The inability of B2 to yield in this “plastically hard“ direction was accompanied by an unusual stress accumulation in the surrounding matrix of ferrite with which the B2 precipitates hold a cube-on-cube orientation relationship. Accordingly, the microstresses based on \{200\}_bcc were greater than those based on \{110\}_bcc and \{211\}_bcc reflections. The latter observation differentiates the present case from the behavior of B2-free ferrite in ferritic or duplex steels and provides a likely explanation for the facilitated occurrence of \{100\}_bcc cleavage in B2-strengthened ferritic and martensitic steels.