Inês Pérez de Castro (c. 1320 - 1355) was cousin and lady-in-waiting to Infanta Constança of Castile, who was to marry Dom Pedro, son of King Afonso IV and heir to the Portuguese throne. Dom Pedro fell in love with Inês, and although he still married Constança he carried on a lifetime affair with her, and they had several children together. This was an era of fragile relations between Portugal and Castile, and Inês was seen as a damaging influence, leading to Afonso eventually ordering her execution. Pedro was heartbroken, and on becoming king had her assassins tracked down, tortured and killed. He then claimed that he and Inês had been secretly married several years before her death, and therefore Inês was his legal wife and lawful Queen of Portugal. Pedro then had her body exhumed and moved to a tomb in the Monastery of Alcobaça. Versions of Inês' story differ greatly, as history becomes entangled with legend. One version has Pedro placing the exhumed corpse of Inês on the throne, crowning her Queen, and forcing courtiers to kiss her hand in a show of allegiance. A full version of Inês' story is told here.
On page 7 of Possession, Byatt tell us that Randolph Ash wrote a poem about 'Pedro of Portugal's rapt and bizarre declaration of love, in 1356, for the embalmed corpse of his murdered wife, Iñez de Castro, who swayed beside him on his travels, leather-brown and skeletal, crowned with lace and gold circlet, hung about with chains of diamonds and pearls, her bone-fingers fantastically ringed.'