Fiona O'Beolan

Second, having had two natural sons, John and Donald, by one whom Sir Robert designs "a woman of the western isles," he married her in order to legitimate his sons;  and afterwards obtained from the king, a precept of legitimation in their favour the tenor of which warrants the conclusion, that their parents were married ; for they are designed "sons of Odo Makky of Strathnavern," and not natural sons or bastards, as was usual, where the parents were not married. Some years before the date of that precept, Adam Gordon had been forming his plans to secure the earldom and estate of Sutherland to himself; and finding that lye Mackay was opposed to his measures, he applied to his brother Niel- Naverach, promising to support his claim to the succession, as John and Donald were accounted illegitimate : which Iye Mackay having discovered, he banished his brother Niel and his family from his country; and as Adam was also courting the friendship of Caithness, Niel went thither to reside. It is highly probable, that it was after his discovery of the plot laid between Adam and Niel, that Iye  Mackay procured the precept from the king. 

"Precept of Legitimation of John and Donald Makky brethren, sons of Odo Makky of Strathnavern, &c. in due form, with new additions, &c. At Edinburgh, 8th August 1511, and of the king the 24th year."-Privy Seul, B. 4. Fol. 145. pg. 99
HISTORY THE HOUSE AND CLAN MACKAY...;ROBERT MACKAY; 1829.

In the Scottish Peerage pg. 162 she is describded as "According to the Knock MS.,' he married a daughter of Norman, son of Patrick O'Beolan of Carloway, Lewis, a very beautiful woman ; and Gordonston ' describes her as ' a woman of the West Yles.' The marriage was, however, not canonical, for he had a precept of legitimation for his two surviving sons, John and Donald, 8 August 1511.'"