I don’t know how many of you have read the book, but here’s the deal: Frollo had a little brother named Jehan. And though Frollo is pretty cold and uncaring toward everyone else, he adored his baby brother. He practically raised the kid after their parents died, but despite this, Jehan was his opposite. Frollo spoiled him; he could never say no. And so Jehan never went to class, and he drank and gambled and was a general hooligan. He’d show up every couple of weeks to ask for money with increasingly ridiculous excuses.
And then Jehan died while involved in some gypsy scheme.
I think this is what happened in the movie — just before even the prologue. I think this is what drove Frollo to loathe gypsies so deeply. It would also explain why he was so harsh on Quasimodo. He let Jehan get away with everything, and he failed; his brother died. So he kept Quasimodo under an insanely iron rule and would not let the child do anything.
Oh that is super interesting. Thanks for the headcanon.