By the end of the thirteenth century, when the Yorkshire Bruses had passed into oblivion, the Scottish Bruses were ascending towards their historic climax, beginning with the Great Cause in 1292 when Robert de Brus V, ‘the Competitor’, narrowly lost the kingship of the Scots to John de Balliol, his cousin's son, and coming to fruition in the person of his grandson, King Robert I. But the seeds of that achievement had been sown in the early years of the century, when the son of William de Brus, lord of Annandale, was married to Isabel, second daughter of Earl David of Huntingdon and niece of King William the Lion.

It is by no means certain that the marriage between Robert de Brus IV and Isabel of Huntingdon took place in the lifetime of William de Brus, who had died by 1212. According to Fordun, Earl David ‘gave his daughter in marriage’ which places it before 1219, a date compatible with Robert IV's heir, Robert V, being of age by 1242 at the latest. It has been suggested that the marriage took place as early as 1210, thus linking it with the marriage of Earl David's eldest daughter, Margaret, to Alan of Galloway in 1209. Although there is no firm evidence for this, it is highly plausible that the marriage was at least arranged at that time, even if it did not take place immediately.