I would then state he needs to pay back his parents for their child support in return, as what is good for the goose is good for the gander.

In short, my view is no. If the child was biologically his, and he signed for it at minute zero of her first breath of air, he is "in it to win it" for the 18 years.

Where things "might" get legally interesting (but not pertinent here), is if the child was not his and he was lied to by the wife., but then the prime person would be the ex and not the child.