Robert married ca. 1219 Isobel of Huntingdon, the second daughter of David of Scotland, 8th Earl of Huntingdon, by which marriage he acquired the manors of Writtle and Hatfield Broadoak, Essex in England. They had his heir and successor, and a daughter: Robert de Brus, 5th Lord of Annandale. Bernard de Brus Through her came the claims firstly of her son in 1290 and later in the beginning of 14th century of her great-grandson Robert Bruce, 7th Lord of Annandale, to the Scottish throne. Her above-mentioned son Robert Bruce, 5th Lord of Annandale was regent and recognized heir presumptive of Scotland in the years just before her death.