Lens flare

Could be classed as a bit of a school boy error as I was aware of the sun moving as we were outside for an hour, Even the subject blinking, but i'd taken my eyes off the subject as I took the image and even thought at the time in the back of my mind that I was sure he blinked.

Lens flare is created when non-image forming light enters the lens and subsequently hits the camera's film or digital sensor. This often appears as a characteristic polygonal shape, with sides which depend on the shape of the lens diaphragm. It can lower the overall contrast of a photograph significantly and is often an undesired artifact, however some types of flare may actually enhance the artistic meaning of a photo. Understanding lens flare can help you use it — or avoid it — in a way which best suits how you wish to portray the final image.

http://www.cambridgeincolour.com/tutorials/lens-flare.htm