During these transactions at Winchester, there appeared a star of wonderful magnitude and brightness, darting forth a ray, at the end of which was a globe of fire in form of a dragon, out of whose mouth issued forth two rays; one of which seemed to stretch out itself beyond the extent of Gaul, the other towards the Irish Sea, and ended in seven lesser rays.

At the appearance of this star, a general fear and amazement seized the people; and even Uther, the king's brother, who was then upon his march with his army into Cambria, being not a little terrified at it, was very curious to know of the learned men, what it portended. Among others, he ordered Merlin to be called, who also attended in this expedition to give his advice in the management of the war; and who, now being presented before him, was commanded to discover to him the significance of the star. At this he burst out into tears, and with a loud voice cried out, "O irreparable loss! O distressed people of Britain! Alas! the illustrious prince is departed! The renowned king of the Britons, Aurelius Ambrosius, is dead! whose death will prove fatal to us all, unless God be our helper. Make haste, therefore, most noble Uther, make haste to engage the enemy: the victory will be yours, and you shall be king of all Britain. For the star, and the fiery dragon under it, signifies yourself, and the ray extending towards the Gallic coast, portends that you shall have a most potent son, to whose power all those kingdoms shall be subject over which the ray reaches. But the other ray signifies a daughter, whose sons and grandsons shall successively enjoy the kingdom of Britain."

Geoffrey of Monmouth's Historia Regum Britanniae