The following outline of the story is modified and supplemented from other sources.

The real Merlin is said to have been a bard of the fifth century, and is supposed to have served the British chief Ambrosius Aurelianus, and then King Arthur.

This Merlin lost his reason after the battle of Solway Firth, broke his sword, and retired into the forest, where he was soon after found dead by a river bank.
The mythical Merlin had a more exciting and interesting career, however.
King Constans, who drove Hengist from England, was the father of three sons,--Constantine, Aurelius Ambrosius, and Uther Pendragon.

When dying he left the throne to his eldest son, Constantine, who chose Vortigern as his prime minister.

Shortly after Constantine's accession, Hengist again invaded England, and Constantine, deserted by his minister, was treacherously slain.