In Prometheus, the ancient was orally violated by the mutated octopus-like love child of Elizabeth Shaw. After its progeny bursted from the ancient's chest it resulted in the original Alien creature that first appeared with Ripley.
Now since there is Aliens vs. Predators which never has been taken seriously compared with the original story line in my opinion, but I have to know, has there been a case where a similar mutation occurred with Predators?
That would have to be a very bad-ass combo although I have to lower myself in IQ by asking that.