An aerofoil component of a gas turbine engine, the component having an aerofoil portion which spans, in use, a working gas annulus of the engine, the aerofoil portion having: a pressure side outer wall and a suction side outer wall which respectively define the external pressure side and suction side aerofoil surfaces of the aerofoil portion, each outer wall extending from the leading edge to the trailing edge of the aerofoil portion; one or more main passages which extend in the annulus-spanning direction of the aerofoil portion and which receive, in use, a flow of coolant therethrough; one or more suction wall passages which extend in the annulus-spanning direction of the aerofoil portion and which receive, in use, a flow of coolant therethrough, each suction wall passage being bounded on opposing first sides by the suction side outer wall and an inner wall of the aerofoil portion, the inner wall separating the suction wall passages from the main passages; and a plurality of dividing walls which extend between the suction side outer wall and the inner wall, each suction wall passage being bounded on opposing second sides by a pair of the dividing walls, one of the pair of the dividing walls being closer to the leading edge and the other of the pair of the dividing walls being closer to the trailing edge; wherein the dividing walls have fillets to smooth the transitions from the dividing walls to the inner wall and the suction side outer wall, wherein the length of the inner wall on the transverse cross-section is increased relative to the length of the suction side outer wall and the inner wall curves into the suction wall passages, characterised in that, the fillets are shaped, such that on transverse cross-sections to the annulus-spanning direction of the aerofoil portion, the radii of curvature of the fillets are equal, within ± 25%, to the thickness of the suction side outer wall, to give each suction wall passage a kidney-bowl shape on the transverse cross-sections a pressure side outer wall and a suction side outer wall which respectively define the external pressure side and suction side aerofoil surfaces of the aerofoil portion, each outer wall extending from the leading edge to the trailing edge of the aerofoil portion; one or more main passages which extend in the annulus-spanning direction of the aerofoil portion and which receive, in use, a flow of coolant therethrough; one or more suction wall passages which extend in the annulus-spanning direction of the aerofoil portion and which receive, in use, a flow of coolant therethrough, each suction wall passage being bounded on opposing first sides by the suction side outer wall and an inner wall of the aerofoil portion, the inner wall separating the suction wall passages from the main passages; and a plurality of dividing walls which extend between the suction side outer wall and the inner wall, each suction wall passage being bounded on opposing second sides by a pair of the dividing walls, one of the pair of the dividing walls being closer to the leading edge and the other of the pair of the dividing walls being closer to the trailing edge; wherein the dividing walls have fillets to smooth the transitions from the dividing walls to the inner wall and the suction side outer wall, wherein the length of the inner wall on the transverse cross-section is increased relative to the length of the suction side outer wall and the inner wall curves into the suction wall passages, characterised in that, the fillets are shaped, such that on transverse cross-sections to the annulus-spanning direction of the aerofoil portion, the radii of curvature of the fillets are equal, within ± 25%, to the thickness of the suction side outer wall, to give each suction wall passage a kidney-bowl shape on the transverse cross-sections