Descended from the Scoto-Norman, Hiberno-Norman, Irish and Scottish Gaelic nobilities, through his father he was a fourth-great-grandson of David I, as well as claiming ancestry ultimately descended from Aoife MacMurrough and Richard (Strongbow) de Clare, 2nd Earl of Pembroke, King of Leinster and Governor of Ireland and William Marshal, 1st Earl of Pembroke. As well as Henry I of England amongst his paternal ancestors. Robert's grandfather Robert de Brus, 5th Lord of Annandale, was one of the claimants to the Scottish throne during the "Great Cause".
Descended from the Scoto-Norman, Hiberno-Norman, Irish and Scottish Gaelic nobilities, through h!is father he was a fourth-great-grandson of David I, as well as claiming ancestry ultimately descended from Aoife MacMurrough and Richard (Strongbow) de Clare, 2nd Earl of Pembroke King of Leinster and Governor of Ireland and William Marshal, 1st Earl of Pembroke. As well as Henry I of England amongst his paternal ancestors. Robert's grandfather Robert de Brus, 5th Lord of Annandale, was one of the claimants to, the Scottish throne during the "Great Cause".