Is there a legend of a monster in prince of wales?

There was supposed to be a monster in the family history of his grandmother, the Queen Mother.

Apparently there was a son born to this noble line who was a sort of wild monkey covered in hair, and he was kept in a secret room at Glamis Castle. Curious visitors would count the Windows from the outside, and work out that one of them could not be reached from inside.

However, some people think that the story may have been embellished, or made up entirely, because this remote castle would encourage legends, and on the long winter evenings, they would be inclined to tell dramatic stories.