A combustor for a gas turbine engine, comprising: a plurality of primary nozzles configured to diffuse fuel into an air flow through the combustor; and a secondary nozzle configured to premix fuel with the air flow, the secondary nozzle comprising a fuel passage extending downstream in the combustor and having a downstream end portion, a center body provided around the fuel passage, a burner tube provided around the center body and defining an annular air-fuel mixing passage between the center body and the burner tube, the burner tube having an inlet open to a volume of air flow; at least one vane in the annular air-fuel mixing passage upstream of the downstream end portion of the fuel passage and configured to swirl the air flow, further including a chamber upstream of the at least one vane; and at least two cooling passages comprising a fuel cooling passage to cool surfaces of the center body and the at least one vane, and an air cooling passage to cool a wall of the burner tube, wherein the fuel passage is configured to pass fuel in a downstream direction of the combustor, and the fuel cooling passage has an inlet proximate to the downstream end of the fuel passage and an outlet open to the chamber, the center body being provided around the fuel passage defining a reverse fuel passage configured to pass fuel in an upstream direction of the combustor to cool the outer surface of the center body, the fuel cooling passage comprising the reverse fuel passage, wherein the at least one vane includes the cooling chamber configured to receive fuel from the reverse fuel passage, an outlet chamber configured to expel the fuel through at least one fuel injection port in the at least one vane into the fuel-air premixing passage, wherein the fuel cooling passage further comprises the cooling chamber, characterized in that the air cooling passage is open to the volume of air flow provided to the burner tube, the at least one divider is provided between the cooling chamber and the outlet chamber to define a non-linear fuel path, wherein the fuel cooling passage further comprises the non-linear fuel path, wherein the at least one divider is provided with a by-pass hole configured to permit fuel flow directly from the cooling chamber to the outlet chamber. a plurality of primary nozzles configured to diffuse fuel into an air flow through the combustor; and a secondary nozzle configured to premix fuel with the air flow, the secondary nozzle comprising a fuel passage extending downstream in the combustor and having a downstream end portion, a center body provided around the fuel passage, a burner tube provided around the center body and defining an annular air-fuel mixing passage between the center body and the burner tube, the burner tube having an inlet open to a volume of air flow; at least one vane in the annular air-fuel mixing passage upstream of the downstream end portion of the fuel passage and configured to swirl the air flow, further including a chamber upstream of the at least one vane; and at least two cooling passages comprising a fuel cooling passage to cool surfaces of the center body and the at least one vane, and an air cooling passage to cool a wall of the burner tube, wherein the fuel passage is configured to pass fuel in a downstream direction of the combustor, and the fuel cooling passage has an inlet proximate to the downstream end of the fuel passage and an outlet open to the chamber, the center body being provided around the fuel passage defining a reverse fuel passage configured to pass fuel in an upstream direction of the combustor to cool the outer surface of the center body, the fuel cooling passage comprising the reverse fuel passage, wherein the at least one vane includes the cooling chamber configured to receive fuel from the reverse fuel passage, an outlet chamber configured to expel the fuel through at least one fuel injection port in the at least one vane into the fuel-air premixing passage, wherein the fuel cooling passage further comprises the cooling chamber, characterized in that the air cooling passage is open to the volume of air flow provided to the burner tube, the at least one divider is provided between the cooling chamber and the outlet chamber to define a non-linear fuel path, wherein the fuel cooling passage further comprises the non-linear fuel path, wherein the at least one divider is provided with a by-pass hole configured to permit fuel flow directly from the cooling chamber to the outlet chamber.