6:40 as a last train sounded awfully uncivilized so I checked with my sis:
De laatste trein op zondagen in april van Roubaix naar Parijs vertrekt om 20h17 en is een rechtstreekse trein (eerdere reizen zijn met 1 overstap), die er anderhalf uur over doet. Andere tijden kunnen opgezocht worden op http://www.voyages-sncf.fr .
Which translates as last train on Sundays in April from Roubaix to Paris leaves 20:17 and is a direct train (earlier trips have one transfer) taking 1.5hrs for the trip. Other departure times can be looked up at http://www.voyages-sncf.fr
(while we have exercised reasonable skill, care, and diligence to assess the data acquired during the preparation of this information, we make no guarantees or warranties as to the accuracy or completeness thereof)
Only a girlfriend and already a widow :-)