What do I call my fiance's parents?

iamsteph

When I met FI parents 7ish years ago, I called them Mr and Mrs at that meeting. His Dad was like ''nono call me by my first name" and so I did, and his mom didn't say anything, so Mrs. it was.  A year or so later, when I called him by his first name (and after he figured out he didn't like me I guess), he asks ''when did I ever ask you to call be by my first name?''. I told him exactly when he did, but it was awkward, and ever since, it's been Mr. 

We've been together for 8 years now and getting married in a few months. Everyone else in his family calls them by their first names, except me (he of course calls them mom and dad).  I guess I'll still be calling them Mr. and Mrs in twenty years :P