 Louis persuaded the most influential Polish lords to swear an oath of loyalty to her younger sister, Mary, in September 1379.She was betrothed to Sigismund of Luxemburg, a great-grandson of Casimir the Great, who had been Louis's predecessor on the Polish throne.The "promised marriage" of Jadwiga and William was confirmed at their fathers' meeting in Zólyom (now Zvolen in Slovakia) on 12 February 1380.