You said you parted on good terms and that he even attended your wedding right? Well that to me sort of states that he knows you have moved on.
I would treat it as any old friend getting in touch, if you have his e-mail drop him a line, say you where suprised to here from him after all this time, you hope that he is well and then tell him a little about where you are, something simple like, still married and still in love with DH, have X amount of kids and X amount of Chickens... Keep it ligh hearted and show your husband what you are going to send him.
Then if he writes back be open with your husband as to what he writes.
I had a ex try and contact me once, I was in a relationship and worried about it and just ignored it, found out later that he had died, he had cancer and just wanted to reconnect with friends (he was married with two kids) he told his wife that he regerted never getting the chance to say goodbye to me as we had been friend for a long while before we became something more.
I am not saying this is the case with him but maybe it is just someone getting in contact just to be friends.