I didn't tell my family because I didn't want them to go through the expense and I didn't want any fuss. I am wondering if he thought you would have moved heaven and earth to get to the wedding which would mean lots of expense etc?
And I know this sounds insane - but men just don't think the same way as us. They are almost of the frame of mind of, pick a date and I will turn up, as opposed to the bride and rest of the females who want to make an event of it. It may not have registered in his mind that he should have told you and he probably just dropped it into conversation with those who now know.
Tell him that you will get yourself a bottle of bubbles and, on the day, you will raise a glass to him and his lovely bride. Be excited for him. Put away your own disappointment and hurt, if you can. Tell him you want to see lots of pics.
I hope you don't think I am just wittering on - I am trying to make the best of it for you and for your future relationship with your son and new daughter, because that is what is really important.