A turbine stator vane with an airfoil extending between an inner endwall and an outer endwall, and with a fillet formed between the airfoil and each of the endwalls, and a row of metering impingement and diffusion slots extending around the leading edge region and along the pressure side and suction side of the airfoil just below the fillet that discharges a layer of film cooling air onto the surface of the endwall. A showerhead arrangement of film cooling holes in the leading edge region of the airfoil also discharges a layer of film cooling air toward the leading edge fillet in order to form a double layer of film cooling air from the leading edge region of the endwall.