Nope. Only the admission of a new state, or the creation of a new state within an existing state, or from merger of two states, or a new state from parts of existing states. It is absolutely silent about a state reducing it's borders or removing itself from the union.
Titles of nobility are forbidden by the Constitution.
Please note, my comment indicated the "monach" was elected, not hereditary titled.
The Constitution reserves powers to the United States, and some of those may be implied from the Constitution.
Wrong. The Constitution reserves "delegated" (capable of being resumed) powers to the states, not to the federal government.
If you create a new state from uniting two other states, then that removes one state from the Union and requires Congressional approval. Removing a state through secession should be no different.
Please note, my comment indicated the "monach" was elected, not hereditary titled.
But still a title of nobility and therefore covered by the Constitution. Titles don't have to be hereditary, the U.K. grants individuals titles of nobility which are not passed on to the next generation, Margaret Thatcher is an example of that.