I think its pretty customary to invite the European royal Heads of State so Monaco would have been included. Albert shows up now and then but almost always without his wife who does not seem to be up for the task of representing her country abroad nor the House of Grimaldi for that matter. She only glitters and does engagements in her own principality and the number of times an be counted on one hand. Caroline, as Princess of Hanover, was invited to royal parties for some a period of time but that seems to be in the past as well. Awkward family..