Once upon a time, a long time ago, there was a King, Queen and Prince. The Prince, by law, was to marry a Princess, but there was none to be found that suited him.
One stormy night, a young woman came to the castle. She was separated from her family in the storm and needed shelter. The King and Queen agreed to allow her to spend the night. She told the Queen she was a Princess, but you could not tell by her tattered clothes and tired body. The Queen, wanting to know for sure, placed a pea under 20 mattresses and 20 feather beds, knowing that a true Princess was extraordinarily sensitive and wouldn't be able to sleep.
The next morning, the Princess said she felt like she was sleeping on a rock, and was surprised for she thought 20 mattresses would provide a wonderful sleep. The Queen was elated, and told the Prince (who had already fallen in love with the Princess). He told the Queen that he already knew she was a real Princess by "the gentleness of her eyes, the softness of her voice and the kindness of her heart".
And, the Queen told the girl that she could spend the night at their castle.
She prepared 20 mattresses with 20 feather beds. Then, she placed a single pea under the lowest mattress.