You're operating under the assumption that alien means drastically different from human, but they don't have to be.
Also, could just go secret government cover up, and that Dahlia is really just his handler now that he is older and is being swarmed by ladies.
It could be space magic that no human understands.
It could be gas from Jupiter caught the rays of the sun, bounced off a secret satellite launched by the soviet union back at earth and irradiated him to cause the change.
I said it a few days ago, it doesn't need to be that deep... it doesn't have to be deep at all. It does need to be entertaining though.