 He proposed to marry Margaret, daughter of Amadeus IV of Savoy, but her grandfather Thomas I refused to grant the marriage while she was still very young.The two were wed in December 1235 at Chivasso, his capital, and Margaret became the mother of the future William VII and of Alessia (Alessina, Adelaide, Adelheid), future wife of Albert I, Duke of Brunswick-Lüneburg and Gerhard I, Count of Holstein-Itzehoe.Amadeus appears to have concluded an agreement with Boniface whereby the latter would succeed to his Alpine Piedmontese lands if the Savoyard died without heirs.