I'm pretty sure I saw something like that on Lit. It was a passing reference at the end of the story if I remember correctly, an 'oh by the way ...' instead of a major plot point. But I have no idea what the rest of the story was, could even have been a different one than what you're thinking of.

Was it Brad the Bully fucks my mom? I recall in one of the later chapters of part 2 that the slut mommy gives Brad photos of herself and cash even though they are struggling financially?

There was also a story called Netorare Mommy by matthew_elizabeth where the cuck dad left everything for the mom and the bully lover such as the house, savings account and everything to the bully and nothing for the son?

I reread Brad the Bully and that's not the one. I'm still looking for it.