Dunstonbury was traditionally the ancestral seat of House Manderly, but they abandoned it a thousand years prior to the War of Conquest when they fled the Reach. Eventually the Manderlys settled under the dominion of House Stark in The North where they built the New Castle, which they designed similarly to Dunstonbury.
The castle was given to the rivals of the Manderlys, House Peake, who already held their own ancestral castle of Starpike. House Peake sided with King Daemon Blackfyre during the First Blackfyre Rebellion and after defeat were stripped of two of their castles, Dunstonbury and Whitegrove, leaving only Starpike. It is unknown who the current lord of Dunstonbury is.