No, the Royal Wedding is too obvious. They’ll go for a softer and more unaware target. It might very well be the same day what with all eyes on London though. That said, they might have one or two small diversions in London earlier in the day just to keep the eyes of the world away from the real deal.
My first instinct was Russia. Russia just killed one of their top commanders, and they are hellbent on revenge. It appears that some of these groups purchased chemical weapons from the rebels in Libya. Very uneasy these days.