The
Archprelacy was originally rolled into the Governorship of Chesley when Duke Baxter Iracor I of Chesley assumed the chair as Archprelate Maximilian I. At the time, Maximilian had been the third most powerful man in the Imperium, next to Crown Prince Carados and the Emperor himself, and the concession was made that his secular holdings would continue to be held throughout his Archprelacy, as there was no heir or issue of House Iracor to take on the Ducal mantle.
When the Archprelate's rebellion against the Crown took place and the Chesleyan holdings were either destroyed or absorbed into the new Arium, the newly reformed College of Prelates elevated Vesta to the Archprelacy. Carmelyn was set aside in a Crown decree as the new grant to the Faith, as Chesley itself was a burned husk of a ruin and the Crown knew that, focused on building an entire 'holy city' of Diana from the foundation, the Faith would have need of those of its members that would rather have been out denouncing the Crown's actions in the Chesleyan Affair to provide labor. Vesta, being very much invested in the reforms, very graciously complied, and haughty zealots spent the remainder of their days making Diana a city fit to be a capital for the Faith.
Since then, Carmelyn's Governorship has been firmly attached to the post of the Archprelacy. When the Alyssan reforms came down, even Empress Alyssa was not so bold as to try and secularize Carmelyn, but merely integrated it into her Provincial government, with the Archprelate acting as Governor.
Imperial Government Finalization Discussion