(For record keeping purposes, both the Prince and Princess are of whatever the age of consent plus three is in your local laws.)
Once upon a time, there was a kingdom far away that had a King, a Queen, and a Prince. The royal family found themselves distraught since the Prince refused to marry any but the most noble of princesses. He had met many so-called princesses but had always found himself unsure of the truth of their identity.
The first girl he had courted claimed to be a princess based on her pale white skin, but the Prince has learned that she powdered and made her skin up. He decided that a true princess would not feel the need to lie to prove her worth.
The next to try said she was a princess and offered as proof her cooking, but when they sat to eat the food she casually grabbed handfuls of potatoes and meat and shoved food in her mouth, and the Prince told her to leave because a true princess could not have such atrocious table manners.
Others came and tried, and the Prince was ready to give up on finding a true princess, brooding in his library on a rainy day, when he heard a servant hurry past towards the front door of the castle.
Curious who could be calling at such an hour and in such a storm, the Prince followed along, thinking to greet the guest himself and, if need be, see them off without bothering his parents.
When the servant opened the door, in the entrance hall stood a young woman, drenched to the bone and with her heaving breasts uncovered. She had clearly been running, no mean feat between her large breasts, the heeled shoes, and the uneven cobbles outside.
"Please," she was saying "please let me in. I've come so very far, and my traveling companions and I were attacked on the way here. I am the Princess of a faraway kingdom and have come to meet your prince."
The door guard offered the girl a wrap from a hook by the door, and turned to find the King and Queen, but ran into the Prince instead.
"My Lord, this young woman claims to be a Princess come to meet you. Shall I take her to your parents?"
The Prince was already somewhat smitten and, having seen so much of her body, very much hoped her story was true. "No, Jarvis. Please inform my parents of her arrival, but I would like to speak with her myself."
"Yes, my lord." The loyal manservant turns and leaves the room, off to find the King and Queen.
**
"I don't like it." The Queen says to her husband. "This hussy turns up here, in a storm, and without a top? She says they were attacked, but how do we know that wasn't a lie."
The weariness in the King's face extends to his voice as he listens to his wife rant about the situation for the fifth time this evening. "Why don't you devise a test of some sort then. Some way to prove whom she is?"
The Queen smiles at her husband's idea. She would devise an impossible test and get rid of this little hussy once and for all.
I shall set her up in Grandmother's old room, and place something under the mattresses. I'll tell our foolish son that if she wakes with a pain in her back, that she is a true princess. Otherwise, he must cast her out.
**
Shortly thereafter, the Queen puts her diabolical plan into motion. First, she goes to the Princes quarters, and tells him of her test. He agrees, thinking that her logic must be sound, since she was a princess once.