The Duchy of Faercrest is/was a duchy in the Lord Paramouncy of Thyllanor. Officially, the title does not exist in the Lord Paramouncy due to reforms brought about by former Lord Paramount Malveus II Karthmere in the late 3rd century AC that established a larger government under the Lord Paramount and bureaucratic branches within it; prior to that, the title existed in full regard for hundreds of years, always being the seat of Thyllanor from the duchy's namesake, the city of Faercrest.
For representative purposes, however (and to the rest of Andoras), the title is still used to represent what is now called the Royal Demesne of Thyllanor. In its history as a duchy under Thyllanor, it has always been ruled by House Karthmere. Its current ruler is Dalan II Karthmere, whom is also the current Lord Paramount -- athough the title of Lord Paramouncy might soon expire as Thyllanor moves towards a proper traditional monarchy, as a Kingdom.