[The Squatter of Amon Rûdh]

Christopher Tolkien puts it this way:

[Berúthiel] was the nefarious, solitary and loveless wife of Tarannon, twelfth king of Gondor (Third Age 830-913) and first of the 'Ship Kings', who took the crown in the name of Falastur 'Lord of the Coasts', and was the first childless king... Berúthiel lived in the King's House in Osgiliath, hating the sounds and smells of the sea and the house that Tarannon built below Pelargir 'upon arches whose feet stood deep in the wide waters of Eithir Anduin'; she hated all making, all colours and elaborate adornment, wearing only black and silver and living in bare chambers, and the gardens of the house in Osgiliath were filled with tormented sculptures beneath cypresses and yews. She had nine black cats and one white, her slaves, with whom she conversed, or read their memories, setting them to discover all the dark secrets of Gondor, so that she knew those things 'that men most wish to keep hidden', setting the white cat to spy upon the black, and tormenting them. No man in Gondor dared touch them; all were afraid of them, and cursed when they saw them pass.

Berúthiel's name was erased from the Book of the Kings, and Tarannon set her adrift with her cats "before a north wind". The younger Tolkien continues: "The ship was last seen flying past Umbar under a sickle moon, with a cat at the masthead and another as a figure-head on the prow."

You can find this description in Unfinished Tales, in the seventh note to the chapter entitled The Istari.