You can have the same experience when it goes the other way: someone who is a good friend ends up with a startling revelation that makes your jaw drop.
My case in point was this week: I was hanging out with an academic friend of mine at a conference. He lives somewhat far away, and when I do roll through town, we usually just grab a beer rather than see his house. This week, however, he revealed something that hitherto I had not known. We were talking about how the town the conference was in was sort of shady (sorry Reno) and he mentioned "Yeah, I should have brought my Glock, just in case."
"Pardon?"
"Oh yeah. Did I not tell you? I have guns. Lots of guns."
As a leftie even in Britain, and someone who is scared of even the mention of guns, this was a bit of a surprise. The difficulty/trick, I guess, is to reconcile the person you have with the person you are now presented with, and realize that they are really one and the same, just with one minor change that makes no difference to your interactions.
This happens to me much more in the US than in the UK; UK people are much of a muchness. Americans run a full-spectrum. I guess this is why politics here is so polarized.