The Leabhar Chlainne Suibhne states that Suibhne was the son of Donnshléibhe, son of Aodh Aluinn, son of Anradhán. The account claims that Anradhan was the younger son of Aodh Athlamhan. When his brother succeeded their father, the two brothers quarreled with each other, and Anradhán sailed to Scotland. There he conquered half of the country before making peace with the King of Scots, by marrying his daughter. Suibhne is credited within the account to have built Castle Sween. His son is named as Maolmhuire an Sparáin ('Maolmhuire of the Purse').Everything in that account that can be checked against other sources is wrong, so we're not dealing with an accurate record even by the loose standards of Celtic oral history. Some historians try to make sense of this, but so far as I can it might be pure imagination. Still, somebody built the castle a good while before 1300, and how cool to have a family history called the Leabhar Chlainne Suibhne.
Somehow the castle ended up in the hands of the Scottish king, because in 1376 he granted it to John I, one of the MacDonald Lords of the Isles.They held it to 1490, when it was taken by the MacDonalds' great enemies, the Campbells, who made it part of their Earldom of Argyll.