The Laidley Worm was in fact a woman who had been turned into a monster by an evil queen.
In this form she devastated the countryside around Bamburgh for many years.
Eventually, getting fed up of all this, the 'Childe of Wynde', who was the son of the Northumbrian King, set forth determined to kill the wyrm.
However, much to his astonishment, the wyrm would not enter into combat with him.
Upon reflection it dawned upon him that the monster had more than a passing resemblance to his long-lost sister, and upon this realisation the spell was broken.
So powerful was the spell that on breaking, the evil queen was herself turned into a toad and still lives in a cave under Bamburgh Castle to this day.