Originally Posted by
thumpism
Diamant is the name of an old German-then-East-German producer but yours might be Belgian. The frame sticker does not look like the stickers on the GDR/DDR bikes I found using Google; that lettering has a lean and is more art-y looking.
Here's a Belgian Diamant on eBay and the sticker matches yours.
VDL might signify the last name van de Lippens, and Google turns up a Pieter/Peter who looks like he might have ridden that bike.
Mal is a little town north of Liege near Tongeren in Flanders.
thumpism I have not been able to find info on Peter Van de Lippens. A y chance you can provide a link?