You win the golden apple (what else would you hand out for Iliad quotations). It's from the Achilles quote, of course, though the Apollo one is appropriate, too.

Cousin, my *ass*.

Well, maybe if the Iliad were a V.C. Andrews novel. Or Moll Flanders.
"You mean, I've come all the way to Phthia and fallen in love with you and all this time we've been-"
"Cousins. Yes, I'm terribly sorry, Patroclus. It turns out your mother was my father's illegitimate half-sister, who ran away with a foreign nobleman! Our family never speaks of her, so I didn't learn the terrible secret until just now!"
"But, but that means our marriage is invalid!"
"I'm afraid so. Also, the gods disapprove of incest unles they're practicing it."
"Oh, no! We're doomed!"