An anti-icing system (150; 350), comprising: a first bulkhead (136; 336) and a second bulkhead (138; 338), wherein the first bulkhead (136; 336) is a forward bulkhead and the second bulkhead (138; 338) is an aft bulkhead; a plenum (140; 340); an inner duct having a first end configured to deliver heated gas to the plenum (140; 340) and a second end spaced from the first end, wherein the first end of the inner duct extends into the first bulkhead (136; 336) and the second end extends into the second bulkhead (138; 338); an outer duct circumferentially encompassing at least a portion of the inner duct, wherein the outer duct is connected to the first bulkhead (136; 336) and to the second bulkhead (138; 338) to form a volume between the inner duct and the outer duct and the first bulkhead (136; 336) and the second bulkhead (138; 338); a seal system disposed proximate the second end, the seal system including a flange and a first annular seal having a radially inner end positioned proximate the flange, wherein the flange is disposed on the inner duct; and a vapor seal disposed proximate the radially inner end of the first annular seal, wherein the vapor seal contacts the flange; characterised in that: the anti-icing system (150; 350) further comprises a bellows connecting the outer duct to the second bulkhead (138; 338); the radially inner end of the first annular seal is oriented in a substantially radially inward direction and configured to create a fluid seal; and the vapor seal comprises a second annular seal having a radially outer portion that extends in a substantially forward and radially outward direction to form the vapor seal through contact with the bellows. a first bulkhead (136; 336) and a second bulkhead (138; 338), wherein the first bulkhead (136; 336) is a forward bulkhead and the second bulkhead (138; 338) is an aft bulkhead; a plenum (140; 340); an inner duct having a first end configured to deliver heated gas to the plenum (140; 340) and a second end spaced from the first end, wherein the first end of the inner duct extends into the first bulkhead (136; 336) and the second end extends into the second bulkhead (138; 338); an outer duct circumferentially encompassing at least a portion of the inner duct, wherein the outer duct is connected to the first bulkhead (136; 336) and to the second bulkhead (138; 338) to form a volume between the inner duct and the outer duct and the first bulkhead (136; 336) and the second bulkhead (138; 338); a seal system disposed proximate the second end, the seal system including a flange and a first annular seal having a radially inner end positioned proximate the flange, wherein the flange is disposed on the inner duct; and a vapor seal disposed proximate the radially inner end of the first annular seal, wherein the vapor seal contacts the flange; characterised in that: the anti-icing system (150; 350) further comprises a bellows connecting the outer duct to the second bulkhead (138; 338); the radially inner end of the first annular seal is oriented in a substantially radially inward direction and configured to create a fluid seal; and the vapor seal comprises a second annular seal having a radially outer portion that extends in a substantially forward and radially outward direction to form the vapor seal through contact with the bellows. the anti-icing system (150; 350) further comprises a bellows connecting the outer duct to the second bulkhead (138; 338); the radially inner end of the first annular seal is oriented in a substantially radially inward direction and configured to create a fluid seal; and the vapor seal comprises a second annular seal having a radially outer portion that extends in a substantially forward and radially outward direction to form the vapor seal through contact with the bellows.