In the course of a conversation this afternoon, I told him that I got engaged in college*, long before I met his father. It's no secret, but it was news to him. Once we sorted out that I hadn't actually been married before--his initial misunderstanding--he was more okay with it, although still rather shocked. I think he believed that Himself and I had been together since the beginning of time, to the extent that he'd given it any thought whatsoever. His SOP is to go off and think about things and then come back with questions days later, so we'll see what bubbles up later in the week as a result.
I've told all of my kids that their choice of a partner in life is pretty much THE most important decision they'll make. (It's a lot easier and less destructive to change your mind on anything else.) Consequently, it seems like a good idea to occasionally note that brains and kindness and integrity and the like should also be high on their list of spousal requirements before they get to that stage where hormones kick in and physical appearance is the only thing that matters. I was trying to explain to him that for most people it takes a while and some trial and error to figure out what they need in a partner and what they can't handle, hence the dropping of the bombshell. Luckily for him, since he's not quite 12 yet, he can safely blow me off with his trademark preteen eye-roll at this stage of the game, and he does.
(NB: on a related note, I read somewhere that you should always watch how a date talks to their parents, gas station attendants, shop clerks and restaurant servers, too: it tells a lot about who they are.)
*A long story, but it should tell you something that EVERYONE I knew was relieved when I broke it off. Ouch.