The present disclosure relates to a turbofan engine having: an engine core having a centre axis and comprising in flow series a compressor, a combustor and a turbine; and a bypass duct surrounding the engine core, the bypass duct having a bypass duct exit area (A COLD ) at its downstream end. The engine further comprises an exhaust nozzle assembly comprising: coaxially arranged inner mixer and outer exhaust nozzles, the exhaust nozzle being axially downstream of said mixer nozzle; a core flow duct defined by the mixer nozzle, the core flow duct having a core exit area (A HOT ); and an exhaust duct defined at least in part by the exhaust nozzle downstream of the mixer nozzle, the exhaust duct having an exhaust throat area (A 8 ). The bypass duct exit area (A COLD ) and core exit area (A HOT ) are axially aligned at a mixing plane to form a mixing plane area (A MIX ). The turbofan engine has a transonic thrust condition, a supersonic cruise condition and a take-off condition. In the supersonic cruise condition, the exhaust throat area (A 8 ) is increased relative to the exhaust throat area (A 8 ). In the take-off condition, the core exit area (A HOT ) is increased relative to the core exit area (A HOT ) in the transonic condition, and the bypass duct exit area (A COLD ) is decreased relative to the bypass duct exit area (A COLD ) in the transonic condition.