The media is the fourth estate, what are # 1, 2, & 3?

The legislature, the courts and the President?

1 is the royalty
2 is the commoners
3 is the clergy

(you know I'm a journalist if i know this)

1 is clergy
2 is royalty/nobility
3 is the people.

The Three Estates

When a text is geared toward a particular class of people, it is said to be written ad status, Latin for "to the estate," that is, to everyone in a particular social category (or "estate"). The idea of the "estates" is important to the social structure of the Middle Ages.

Feudal society was traditionally divided into three "estates" (social classes). The "First Estate" was the Church (clergy = those who prayed). The "Second Estate" was the Nobility (those who fought = knights). It was common for aristocrats to enter the Church and thus shift from the second to the first estate. The "Third Estate" was the Peasantry (everyone else, at least under feudalism: those who produced the food which supported those who prayed and those who fought, the members of the First and Second Estates). Note that these "estates" are defined primarily by what one does (as well as by the social class one is born into).

http://cla.calpoly.edu/~dschwart/engl430/estates.html

The idea of an estate is a social/political division of a pre-capitalist society. Estates related fundamentally to status rather than class in traditionally defined economic/social terms, Marx's relation to the means of production. Many historians have described class as coming out of the French Revolution rather than preceding it.
A fairly minor dispute I suppose, in terms of the OP's question. But there is a distinction. I like the rest of your description.

1 The Monarch
2 The Nobility
3 The Clergy

As the word "estate" implies it was about land ownership and therefore power. When it started being defined solely in terms of power and governing, we added the media as the fourth estate. An idea we should keep very much in mind..

Khash.