An aircraft compound engine assembly (10, 210, 310) comprising: an engine core including at least one internal combustion engine in driving engagement with an engine shaft; a compressor having an outlet in fluid communication with an inlet of the engine core, the compressor including at least one compressor rotor connected to a turbine shaft; a turbine section having an inlet in fluid communication with an outlet of the engine core, the turbine section including at least one turbine rotor (26', 27') connected to the turbine shaft; wherein the turbine shaft is configured to compound power with the engine shaft; and wherein the turbine shaft is rotationally supported by a plurality of bearings; wherein the compressor and the turbine section are respectively provided in a compressor module casing and in a turbine module casing; characterized in that all of the plurality of bearings are located between the at least one compressor rotor and the at least one turbine rotor (26', 27') such that the at least one compressor rotor and the at least one turbine rotor (26', 27') are cantilevered; in that the compressor module and turbine module casings (25, 29) are separate from one another and removable from the assembly independently from one another; in that the plurality of bearings are located outside of the compressor module and turbine module casings (25, 29); in that the casings (25, 29) define an enclosure independently from each other; in that the turbine shaft is connected to the engine shaft through a gear train (68, 368, 368') contained in a gearbox module casing (21, 321'), the compressor and turbine section being located outside of the gearbox module casing (21, 321'), the plurality of bearings being contained in the gearbox module casing (21, 321'); and in that the compound engine assembly further includes a lubricant circulation system contained within the gearbox module casing (21, 321') for circulating lubricant to the plurality of bearings. an engine core including at least one internal combustion engine in driving engagement with an engine shaft; a compressor having an outlet in fluid communication with an inlet of the engine core, the compressor including at least one compressor rotor connected to a turbine shaft; a turbine section having an inlet in fluid communication with an outlet of the engine core, the turbine section including at least one turbine rotor (26', 27') connected to the turbine shaft; wherein the turbine shaft is configured to compound power with the engine shaft; and wherein the turbine shaft is rotationally supported by a plurality of bearings; wherein the compressor and the turbine section are respectively provided in a compressor module casing and in a turbine module casing; characterized in that all of the plurality of bearings are located between the at least one compressor rotor and the at least one turbine rotor (26', 27') such that the at least one compressor rotor and the at least one turbine rotor (26', 27') are cantilevered; in that the compressor module and turbine module casings (25, 29) are separate from one another and removable from the assembly independently from one another; in that the plurality of bearings are located outside of the compressor module and turbine module casings (25, 29); in that the casings (25, 29) define an enclosure independently from each other; in that the turbine shaft is connected to the engine shaft through a gear train (68, 368, 368') contained in a gearbox module casing (21, 321'), the compressor and turbine section being located outside of the gearbox module casing (21, 321'), the plurality of bearings being contained in the gearbox module casing (21, 321'); and in that the compound engine assembly further includes a lubricant circulation system contained within the gearbox module casing (21, 321') for circulating lubricant to the plurality of bearings.