Just a simple Facsimile, an imitation as good as an original.

Fax is a 'they' by default, fluidly somewhere between prince or princess, a regal and somewhat vain doppelganger… and a body-double to Princess Celestia in his Equestria. In the era before Twilight, an alicorn has a lot of things on her plate (besides sweets) and there is need for her to be in two places at once.

Enter Facsimile, a changeling noble who owes quite a debt to the Crown, and so who serves to work off that debt by filling in where Celestia herself can't be. Or doesn't want to be.

There are some who might say that Fax had replaced Celestia entirely long ago… but surely that must be just a rumor. Surely.