As reported by Otta Swire in 1963, Grenish Stone Circle is the crowning place of the Pictish Kings, 'the last to be crowned there was King Brude.' This was related to him by his old gardener, who was told by his old granny, who was told by her old granny and who indeed was told by her old granny as well who was a well noted wise woman and witch.
As it was told, when a Pictish King was crowned, it was customary to raise three spirits, and for the king to ask each a question - but the first must be 'What of my reign?'
When Brude asked this question, he couldn't understand the reply; the spirit was that of an Irish champion who spoke only Gaelic, while Brude spoke only the Pictish language. A Druid was on hand to translate, telling Brude that one greater than he would come out of the sea, rule in his kingdom above him, and make him great. The prophecy refers to the coming of St. Columba of course and his conversion of King Brude to Christianity.
As with a number of Otta Swire's stories, it is uncertain if this is a popular tradition or a romantic fiction. In some respects it sounds suspiciously like the revelation to Macbeth of Banquo's royal descendants, although it is of course possible that Shakespeare based his scene on a report of ancient Scottish custom. We'll never know.