It's not in the creative menu nor is it even craftable, and I don't have any other mod that would conflict with MCA. When upgrading from (4.1.5) I got the usual 'missing-blocks' warning, but immediately afterwards the crown was still present. Then I created a new world and the crown disappeared.

Monarch system and all associated items have been removed in order to be reworked in a future update. Please read all changelogs before reporting issues.