There is quite a long string to complete this and if the wedding is likely to go ahead, it may be you actually need to attend it in Val Royeux for it to open up in the Keep. They are on the first floor and I don't think there is a marker for them, you just have to look around.
However, the Keep doesn't always open up properly. There are several quests I have done that it has failed to register. The whole Sutherland string is another one I can think of. May be it has to do with being War Table missions. So go to the right hand menu and ask it to show spoilers. Then you can go in and manually alter the Keep to reflect the fact you have actually done it.