House of Lara
Juan's parents were Juan Núñez I de Lara (d. 1294), head of the House of Lara, and Teresa de Haro, daughter of Diego López III de Haro, the seventh Lord of Biscay and of Constanza de Bearne. Teresa was the sister of Lope Díaz III de Haro and of Diego López V de Haro, both Lords of Biscay.