A fuel injector for a gas turbine engine comprising: a nozzle, and a housing stem for supporting the nozzle in a combustor chamber, the housing stem including an internal fuel conduit for supplying fuel to an inlet of the nozzle, the nozzle comprising: the inlet at an upstream end of the nozzle; a discharge outlet at a downstream end of the nozzle; a fuel delivery passage extending between the inlet and the discharge outlet; an internal annular wall bounding a radially outer side of the fuel delivery passage along a length thereof, whereby such wall is in heat transfer relation with fuel passing through the fuel delivery passage; an external annular wall (94, 96, 119) interposed between the internal annular wall and ambient conditions, the external and internal walls having downstream tip ends that are relatively longitudinally movable at an interface; an internal insulating gap interposed between the internal and external walls to insulate the internal wall from ambient temperature conditions external to the nozzle; and an annular bellows internal to the nozzle, and provided in the insulating gap, the bellows having an upstream end sealingly attached to an upstream portion of one of the internal and external walls, and a downstream end sealingly attached to a downstream portion of the other of the internal and external walls to fluidly separate a thereby isolated portion of the insulating gap from any ambient fluid that may enter into a non-isolated portion of the insulating gap through the interface; wherein the internal annular wall has a fuel inlet opening at its upstream end that receives and connects to a downstream end of the internal fuel conduit of the housing stem. a nozzle, and a housing stem for supporting the nozzle in a combustor chamber, the housing stem including an internal fuel conduit for supplying fuel to an inlet of the nozzle, the nozzle comprising: the inlet at an upstream end of the nozzle; a discharge outlet at a downstream end of the nozzle; a fuel delivery passage extending between the inlet and the discharge outlet; an internal annular wall bounding a radially outer side of the fuel delivery passage along a length thereof, whereby such wall is in heat transfer relation with fuel passing through the fuel delivery passage; an external annular wall (94, 96, 119) interposed between the internal annular wall and ambient conditions, the external and internal walls having downstream tip ends that are relatively longitudinally movable at an interface; an internal insulating gap interposed between the internal and external walls to insulate the internal wall from ambient temperature conditions external to the nozzle; and an annular bellows internal to the nozzle, and provided in the insulating gap, the bellows having an upstream end sealingly attached to an upstream portion of one of the internal and external walls, and a downstream end sealingly attached to a downstream portion of the other of the internal and external walls to fluidly separate a thereby isolated portion of the insulating gap from any ambient fluid that may enter into a non-isolated portion of the insulating gap through the interface; wherein the internal annular wall has a fuel inlet opening at its upstream end that receives and connects to a downstream end of the internal fuel conduit of the housing stem. the inlet at an upstream end of the nozzle; a discharge outlet at a downstream end of the nozzle; a fuel delivery passage extending between the inlet and the discharge outlet; an internal annular wall bounding a radially outer side of the fuel delivery passage along a length thereof, whereby such wall is in heat transfer relation with fuel passing through the fuel delivery passage; an external annular wall (94, 96, 119) interposed between the internal annular wall and ambient conditions, the external and internal walls having downstream tip ends that are relatively longitudinally movable at an interface; an internal insulating gap interposed between the internal and external walls to insulate the internal wall from ambient temperature conditions external to the nozzle; and an annular bellows internal to the nozzle, and provided in the insulating gap, the bellows having an upstream end sealingly attached to an upstream portion of one of the internal and external walls, and a downstream end sealingly attached to a downstream portion of the other of the internal and external walls to fluidly separate a thereby isolated portion of the insulating gap from any ambient fluid that may enter into a non-isolated portion of the insulating gap through the interface; wherein the internal annular wall has a fuel inlet opening at its upstream end that receives and connects to a downstream end of the internal fuel conduit of the housing stem.