Internal combustion engine system, comprising: - an internal combustion engine comprising a cylinder block housing a plurality of cylinders, a first intake manifold connected to a first group of cylinders, a second distinct intake manifold connected to a second group of cylinders and a first, respectively a second, exhaust manifold (8a, 8b) for receiving the exhaust gas emitted from the first, respectively the second, group of cylinders (4a, 4b); - an air inlet line; - an EGR line connected to the first and second exhaust manifolds (8a, 8b); wherein the internal combustion engine system is operable in at least two operating modes, respectively a normal operating mode in which all cylinders are supplied with fuel and a regeneration operating mode, in which the cylinders of the first group of cylinders are no longer supplied with fuel, characterized in that: - the system also includes a mixing unit comprising a four-way valve, said four-way valve having a first inlet connected to the EGR line, a second inlet connected to the air inlet line, a first outlet connected to the first intake manifold and a second outlet connected to the second intake manifold; - the four-way valve is designed so that, in said normal operating mode, the intake gases supplied to the first intake manifold and to the second intake manifold have approximately the same proportion of exhaust gas and so that, in said regeneration operating mode, the intake gas supplied to the first intake manifold only includes exhaust gas, and in that the four-way valve comprises a housing defining an internal chamber, the internal chamber having a first portion in fluid communication with the first inlet and the first outlet of the four-way valve and a second portion in fluid communication with the second inlet and the second outlet of the four-way valve, the first and second portions (38a, 38b) being separated by a central opening, the central opening being selectively closed by a closure element. - an internal combustion engine comprising a cylinder block housing a plurality of cylinders, a first intake manifold connected to a first group of cylinders, a second distinct intake manifold connected to a second group of cylinders and a first, respectively a second, exhaust manifold (8a, 8b) for receiving the exhaust gas emitted from the first, respectively the second, group of cylinders (4a, 4b); - an air inlet line; - an EGR line connected to the first and second exhaust manifolds (8a, 8b); wherein the internal combustion engine system is operable in at least two operating modes, respectively a normal operating mode in which all cylinders are supplied with fuel and a regeneration operating mode, in which the cylinders of the first group of cylinders are no longer supplied with fuel, characterized in that: - the system also includes a mixing unit comprising a four-way valve, said four-way valve having a first inlet connected to the EGR line, a second inlet connected to the air inlet line, a first outlet connected to the first intake manifold and a second outlet connected to the second intake manifold; - the four-way valve is designed so that, in said normal operating mode, the intake gases supplied to the first intake manifold and to the second intake manifold have approximately the same proportion of exhaust gas and so that, in said regeneration operating mode, the intake gas supplied to the first intake manifold only includes exhaust gas, and - the system also includes a mixing unit comprising a four-way valve, said four-way valve having a first inlet connected to the EGR line, a second inlet connected to the air inlet line, a first outlet connected to the first intake manifold and a second outlet connected to the second intake manifold; - the four-way valve is designed so that, in said normal operating mode, the intake gases supplied to the first intake manifold and to the second intake manifold have approximately the same proportion of exhaust gas and so that, in said regeneration operating mode, the intake gas supplied to the first intake manifold only includes exhaust gas, and in that the four-way valve comprises a housing defining an internal chamber, the internal chamber having a first portion in fluid communication with the first inlet and the first outlet of the four-way valve and a second portion in fluid communication with the second inlet and the second outlet of the four-way valve, the first and second portions (38a, 38b) being separated by a central opening, the central opening being selectively closed by a closure element.