Remove shadow in digital photo

I have a photo of my father and mother in law. The person taking the photo stood between the subects and the sun and has cast a shadow onto one of the subjects. I need it removed but couldnt get it done in GIMP or paintshop.

Have aloook and see what you think

To my mind it should be simple - either make the whole of his t shirt in shadow or lighten the affected area I reckon it should be half an hours work max for a pro