A gas turbine engine having a main axis, an engine casing enclosing a compressor section, a combustor and a turbine section defining a main gas path serially extending therethrough along the main axis of the engine, a primary flow passage for channelling a high velocity primary flow and an ejector comprising: a primary nozzle having an annular wall forming part of an outer boundary of an exhaust portion of the primary flow passage, the annular wall having a downstream end defining a plurality of circumferentially distributed radially inner lobes; a secondary nozzle having an annular wall disposed about the primary nozzle, the primary nozzle and the secondary nozzle defining a secondary flow passage therebetween for channeling a secondary flow, the secondary nozzle defining a mixing zone downstream of an exit of the primary nozzle where, in use, the high velocity primary flow and the secondary flow mix together; and a ring mounted to the circumferentially distributed lobes in the exhaust portion of the primary flow passage centrally about the main axis of the engine; characterised in that: the ring is a flow guide ring having an aerodynamic surface extending from a leading edge to a trailing edge respectively disposed upstream and downstream of the exit of the primary nozzle, the aerodynamic surface being oriented to guide the high velocity primary flow into the mixing zone, wherein the aerodynamic surface of the flow guide ring converges radially inwardly towards the main axis in a downstream direction, and the ejector projects from an aft end of the engine casing axially downstream from an engine center body forming an aft end portion of an inner boundary of the main gas path, the annular wall forms an outer boundary of the main gas path for guiding the primary flow, and the flow guide ring is mounted in the main gas path downstream of the engine center body. a primary nozzle having an annular wall forming part of an outer boundary of an exhaust portion of the primary flow passage, the annular wall having a downstream end defining a plurality of circumferentially distributed radially inner lobes; a secondary nozzle having an annular wall disposed about the primary nozzle, the primary nozzle and the secondary nozzle defining a secondary flow passage therebetween for channeling a secondary flow, the secondary nozzle defining a mixing zone downstream of an exit of the primary nozzle where, in use, the high velocity primary flow and the secondary flow mix together; and a ring mounted to the circumferentially distributed lobes in the exhaust portion of the primary flow passage centrally about the main axis of the engine; characterised in that: the ring is a flow guide ring having an aerodynamic surface extending from a leading edge to a trailing edge respectively disposed upstream and downstream of the exit of the primary nozzle, the aerodynamic surface being oriented to guide the high velocity primary flow into the mixing zone, wherein the aerodynamic surface of the flow guide ring converges radially inwardly towards the main axis in a downstream direction, and the ejector projects from an aft end of the engine casing axially downstream from an engine center body forming an aft end portion of an inner boundary of the main gas path, the annular wall forms an outer boundary of the main gas path for guiding the primary flow, and the flow guide ring is mounted in the main gas path downstream of the engine center body.