Clearly your DH didn't have a "Mummy look"! (or didn't want to ask for directions!)

Yep - just regular L chaped brackets. They don't have to be big - just enough to get a screw into the shelf and one into the wall.

To make them as invisible as possible I screw them upside down so that the vertical part is behind the shelves (so you have to move them out a bit first - so is really only practical when they are empty) and then slide the shelves back in and screw the horizontal bit into the top of the shelves.