It was a bare few weeks before the Battle of Flodden between England and Scotland in the autumn of 1513. King James IV was determined to enter England, partly to aid his ally France, which was currently at war with England. The Scots kings implicitly believed in himself as a warrior and could not have known that he would, in a very short time, have the dubious honour of being the last monarch in the British Isles to be slain on a battlefield.
In the evening he went to hear the service in the kirk of St Michael's at Linlithgow, immediately adjacent to his royal palace. Surrounded by the usual crowd of courtiers and servants, the king was a little apart from them all and possibly in a pensive mood when he was approached by a man in a blue gown who began to warn him not to go to war. The figure came out of nowhere and, more remarkably, once his lecture was over, he vanished into thin air. Nobody knows who he was. There was speculation that he was an actor hired by the king's wife Margaret, sister of Henry VIII, who was against the upcoming war. Or the culprit could have been Sir David Lindsay, a man of the court who became a notes playwright and poet.
The historian Lindsay of Pitscottie, writing a few decades after the event, imbues it with mystery and foreboding. It is generally assumed that the messenger was heavenly in origin, though later writers are divided about his exact identity. Some say St James, others St John, and yet others St Andrew the patron of Scotland, of course. The mystery, of course, will ultimately never be solved. I even allow the possibility in my book The Afterlife of King James IV that the event might not have actually happened.
That aside, I gave the variants on all the heavenly contenders for the saintly messenger and thought I had covered all the possibilities. But, lo and behold, I read in a book that the mysterious figure was none other than King Arthur! News to me. It came to late to be included in my book. Would I have included it if I had found it earlier? Er, nah. Some things are just too far fetched, even when relating visions and the miraculous.