Also you can check out Labels Inc. and Rosier 41. They are both 'outlet' stores but with a mix of new and second hand items, mostly Belgian designers but also the big French ones. Sometimes you can find real gems there, but those pieces usually get sold the day they arrive
Once I even found a coat from Demeulemeester from the current season at 60% off. Many of those new items are showroom models etc.
Both shops are owned by the same women and in the same street (I don't know why they just merge them). Rosier 41 is a lot bigger and nicer to shop.
Labels Inc.: Aalmoezenierstraat 4
Rosier 41: Rosier 41 (it's a real trend in Antwerp to name your store/restaurant like the adress
)