A thrust reverser for an aircraft engine assembly, comprising two sub-assemblies configured to surround an engine, each of the sub-assemblies comprising an inner fixed structure, a translating cowl, a torque box, a substantially vertical 12 o'clock bifurcation, and a substantially vertical 6 o'clock bifurcation. At least one of the sub-assemblies comprises at least one separating partition extending between the inner fixed structure, the translating cowl and the torque box of the sub-assembly, the separating partition being rigidly fixed to the inner fixed structure and the torque box, and connected to the translating cowl via a sliding connection.