It is uncertain why Fergus failed to support his grandson against Somairle. The record of the capture of Domnall mac Máel Coluim at Whithorn in 1156, as recorded by the twelfth- to thirteenth-century "Chronicle of Holyrood", and "Gesta Annalia I", may have bearing on Fergus. Domnall appears to have been a son of Máel Coluim mac Alasdair, who was in turn a claimant to the Scottish throne and somehow related to Somairle. Following David's death in 1153, Somairle and Máel Coluim had risen in revolt against a newly inaugurated Malcolm without much success. Domnall's later capture in western Galloway, therefore, could be evidence that the Meic Máel Coluim claimants had attempted to forcefully carve out a power base in western Galloway. However, the fact that the chronicle makes no mention of such conflict in Galloway, coupled with the fact that Whithorn was a spiritual centre rather than a secular power centre, could suggest that Domnall was in the region under less violent circumstances. If so, it is conceivable that Fergus could have originally forged an understanding with the Meic Máel Coluim before pressure from his sons forced him to desert Domnall's cause. The fact that the latter's capture preceded Somairle's coup could suggest that, although Domnall may have been in the midst of securing Gallovidian support, once Somairle's designs against Guðrøðr became apparent, the Gallovdians handed over Somairle's kinsman to the Scots.