Who married John of Castile, Lord of Valencia de Campos?

John of Castile, called the "el de Tarifa" (Spanish: Juan de Castilla "el de Tarifa"; 1262–25 June 1319) was an infante of Castile and León. He was engaged in a decades-long fight for control over the Lordship of Biscay with Diego López V de Haro, the uncle of his wife.

Margarita de Montferrato (1264-1286) Noble piamontesa, hija de Guillermo VII de Montferrato, marqués de Montferrato, y de Isabel de Clare.

María Díaz I de Haro "the Good" (1270–1342) was a Spanish noblewoman of the House of Haro. She was the daughter of Lope Díaz III de Haro who was assassinated by order of the king at Alfaro, La Rioja. She is best known for being the Lady of Biscay and for her lifelong battle against her uncle, Diego López V de Haro, for the title of the lordship of Biscay.