Factual error: There are numerous references made to the Finnish Royal Family, and they even make an appearance. Only problem is, Finland doesn't have a Royal Family.
Factual error: Cedric mentions that the Imperial State Crown contains the "Star of India" and calls it the second largest diamond in the world. The Star of India is actually a star sapphire and is housed in an American museum. In the actual crown is a gem called the Star of Africa, which is the second largest diamond in the world.
Factual error: When King Ralph arrives at the banquet, he is introduced as "King Ralph the First." This is an error as reginal numbers are only assigned when there is a second monarch with the same reginal name, hence "Queen Victoria", not "Queen Victoria I."