Neutron diffraction studies performed on the solid solution of (BiFeO3)1−x(PbTiO3)x reveal a mixture of two nanoscale phases with different crystal structures: a rhombohedral BiFeO3-based phase and a tetragonal PbTiO3-based phase. The ratio of Fe3+ and Ti4+ ions in the two phases is practically constant; only the proportion of the phases changes. The magnetic moments in the BiFeO3-based phase, in contrast to BiFeO3, deviate from the basal plane. The temperature evolutions of the spin components along the hexagonal axis and within the perpendicular plane are different, leading to a spin re-orientation transition. The antiferromagnetic order in the PbTiO3-based phase corresponds to a simple structure with the propagation vector (1/2, 1/2, 1/2). The temperature dependence of the antiferromagnetic moment in the tetragonal phase at x = 0.5 indicates a canted antiferromagnetic order and a net ferromagnetic moment. A strong magnetic coupling between the two constituting phases due to the nanoscale character of the phases and well-developed interface between nanoparticles has been observed. The system of (BiFeO3)1−x(PbTiO3)x demonstrates an interesting scenario, where the proximity effects in the unstable system play a crucial role in the appearance of the unusual magnetic properties.