What kind of parent would even do that? It's sick.

"My daddy's my grandpa!"

Why? Just... Why? They couldn't even have the curtesy or empathy to carry this out while you weren't romantically involved with her? ****, they didn't even consider the emotional ramifications for the kid when they find out- and they always do. OP, I think you need to get a paternity test done- and a good quality one since you and your father are similar on a genetic level, even if you are miles above him morals wise. If the baby IS yours, I would file for sole custody since the behavior your ex seems to display and engage with is indicative that they really are not capable of making good life choices. Courts tend to favor the father when they actually fight for it, at least during divorces that go that far. If the baby isn't yours, look into seeing if there is a way to change any child support fees/payments you have to make to your father being required to make them and if you can get reimbursement on any payments you may have made.

congrats you have a new brother

First time I read this I thought it said her father's, and I retched. Re-read it, it's still pretty ******* grim. You don't need these shitstains in your life, OP. Good riddance to bad rubbish.

Oh god! Ick

That's sick! What a **** she is!

Great, now he can start paying for the child support (if there was any).

It's your half-brother slash son!

This was a plot on Scandal.

If you've been paying child support I'd say take her cheating ass to court, or Jerry Springer, or both.

I'm sorry OP. Thats a really messed up situation. How does one get over being betrayed by a parent.