DHL has, historically, always been pretty tight with ACL. The B4's were actually operated by ACL originally, then transferred to EAT (BRU) before coming full circle and going back to ACL after EAT moved to LEJ and became EAT GmbH.
EAT, as well as DHK, is a wholly owned subsidiary of DHL Express and are the main providers of lift for DHL intra Europe. There are around 60 airlines in total providing lift for DHL around the world.
If you think that's a bit of a mess, you should see the "ownership plague" inside the B4.s. It goes something like "owned by (some bank, usually in the Caribbean), sub-leased to someone else, sub-sub leased to someone else again and operated by ACL. Tax dodging? Nah, why would anyone think that!