During the Should the Stars Fall event, the two Dark Masters were called upon to help free the Hopeslayer; however, Blackthorn had defected and was now part of the Shard Vigils leaving only Vidorian to assist the Shadow Generals.
The two monarchs who refused to take part in the Gauntlet were called upon by Asheron during the event when Bael'Zharon was defeated.
Town Crier tells you, "High-ranking monarchs have been approached by an unknown presence and subjected to grueling tests on a distant island. Apparently this entity, whatever it is, does not think much of our monarchs. Might this have something to do with the frightful apparition in the lightning flashes?"
Samuel, Former Guardian
Samuel, Former Guardian tells you, "A few years back - you see? A few years back, this island was found. Apparently, Monarchs had gone there before Bael'zharon walked the world, as a test. Something like that-"