I decided to do some nectar-making and took my single male Sim on several vacations to France, enough to get him a vacation home. I was aware of the possibility of magical surprise children, but I couldn't figure any way of getting a high enough level visa without interacting with the locals. I was "trading local gossip" when my Sim said "Claudine My-Last-Name just died!" Yes, apparently one of the (now deceased) locals thinks she was married to him. An elder Sim, at that, who shouldn't even be able to have kids! A day or so later, he got the message that his son had died.
I checked his memories, and he has no memory of woohooing with anyone. His romantic reputation shows the number of relationships as 0. Claudine and Sebastien still show up in his family tree, however.
I don't really care if he has a magic son in his family tree, but I was wondering if anyone knows if this will mess up future romantic interactions when I decide to find him a nice girl.