Question: Who is Domhnall Mac Alasdair's paternal grandfather?
Answer: Domhnall mac Raghnaill

Alasdair Mór mac Domhnaill was a younger son of Domhnall mac Raghnaill—the eponymous ancestor of Clan Donald. He first appears on record in 1253, when it is recorded as witnessing a charter by his brother, Aonghus Mór, to Paisley Abbey. According to the 19th century Clan Donald historians Angus and Archibald Macdonald, Alasdair Mór must have been a prominent man as he is the only recorded brother of Aonghus Mór