A combustor for a gas turbine engine comprising: an inner reverse-flow annular combustor liner; and an outer reverse-flow annular sheet metal combustor liner, the outer liner including a long exit duct portion adapted to redirect combustion gases in the combustor towards a combustor exit, characterised in that: said outer liner includes at least two smooth continuous wall portions intersecting each other at a discontinuity provided by a bend in the outer sheet metal combustor liner, the two smooth continuous wall portions providing an upstream wall and a downstream wall relative to the discontinuity, the two smooth continuous wall portions defining an obtuse inner angle therebetween at the discontinuity, the upstream continuous wall having a plurality of apertures defined therein immediately adjacent the discontinuity, the apertures adapted to deliver pressurized air surrounding the outer liner through the outer liner and along the downstream continuous wall, wherein the combustor includes three of said smooth continuous wall portions respectively separated by, and intersecting at, two of said discontinuities, and wherein at least two smooth continuous wall portions comprise a portion of the long exit duct portion. an inner reverse-flow annular combustor liner; and an outer reverse-flow annular sheet metal combustor liner, the outer liner including a long exit duct portion adapted to redirect combustion gases in the combustor towards a combustor exit, characterised in that: said outer liner includes at least two smooth continuous wall portions intersecting each other at a discontinuity provided by a bend in the outer sheet metal combustor liner, the two smooth continuous wall portions providing an upstream wall and a downstream wall relative to the discontinuity, the two smooth continuous wall portions defining an obtuse inner angle therebetween at the discontinuity, the upstream continuous wall having a plurality of apertures defined therein immediately adjacent the discontinuity, the apertures adapted to deliver pressurized air surrounding the outer liner through the outer liner and along the downstream continuous wall, wherein the combustor includes three of said smooth continuous wall portions respectively separated by, and intersecting at, two of said discontinuities, and wherein at least two smooth continuous wall portions comprise a portion of the long exit duct portion. said outer liner includes at least two smooth continuous wall portions intersecting each other at a discontinuity provided by a bend in the outer sheet metal combustor liner, the two smooth continuous wall portions providing an upstream wall and a downstream wall relative to the discontinuity, the two smooth continuous wall portions defining an obtuse inner angle therebetween at the discontinuity, the upstream continuous wall having a plurality of apertures defined therein immediately adjacent the discontinuity, the apertures adapted to deliver pressurized air surrounding the outer liner through the outer liner and along the downstream continuous wall, wherein the combustor includes three of said smooth continuous wall portions respectively separated by, and intersecting at, two of said discontinuities, and wherein at least two smooth continuous wall portions comprise a portion of the long exit duct portion.