This blacksheep of this rich family

I need some help developing this blacksheep character.

Ok so the thing is that he comes from a rich family (not quite old money nor new money), but demonstrates very little personal refinement (he's a good example of the anti-authority slacker character) as oppose to the rest of his family.

This eventually led to him being disowned from the family.

Later on, he manages to gamble his way (although he had a bit of supernatural help) to a wealth equal in magnitude to that of his former family.

Some of his former kin, especially his father, was appalled at this development, for they felt this blacksheep never honestly worked for his fortune and is now setting a bad example for society.

So the question is what made the blacksheep so different from his kin? What can be roots of his rebellious slacker attitude?

Maybe he was suspected (truly or falsely) of being illegitimate? That would make him his father's unfavorite for certain, and if it technically was a possibility, his mother would be rather uncomfortable around him as well.

Maybe he was influenced by another family member that people dislike - an uncle, maybe.

Blacksheep happens. Why bother explaining the origin? Almost all families have one and can relate to it.