Marius Black was the thrid child born to Cygnus Black and Violetta Bulstrode, and he was born a Squib. We know that he was disowned for this fact, and that they probably found this out for a fact when he didn't get a letter to Hogwarts.
My question is, wha did they do with him after this. Did they just drop him on the doorstep of an orphanage one night, knock, and run, or do you think the sent him away to a Muggle school where they did have to see him and didn't have to think about him? Would he have been completely ignored, or allowed to visit home while he was still a child, but once he became an adult, he was on his own?
Thoughts and opinions?