I had originally shot this image as a sequence of three for an HDR shot. I opened the images in HDR Efex Pro and merged the images using the natural method and settings to try and reproduce a real looking image. Nothing made the sun look acceptable though. So I selected the HDR image and the image in the sequence where the sun looked the best in Lightroom and went into the “Edit In” menu and chose “Open as Layers in Photoshop.” Once in Photoshop, I made sure the original image was on top of the layer stack. Then I held the alt key while clicking on the create layer mask button, thus creating a black mask. I then selected a soft brush and painted in the sun and area immediately around it. If more blending is necessary to make the boundary look natural, do a gaussian blur on the mask.
Tada, that creates the image.