There was once an orphan named Mai An Tiêm who earned a meager living helping a nearby elderly couple. He was very humble and believed what he had did not change him.
The king Hùng and his royal court rode through the village that Mai An Tiêm lived in. The king heard stories of his generosity and was warmed and decided to adopt him. He was so loved the King even let him marry his daughter.
Everyone knew the king admired Mai An Tiêm the most out of all his sons. At a party, Mai An Tiêm said that although he is now living wealthily, it does not change who he is.
The youngest prince was jealous of the adopted prince and created rumors about him. The king, feeling betrayed from hearing the rumors, sent Mai An Tiêm to an island in exile. Mai An Tiêm managed to survive on the island.
One day, he saw a bird dropping seeds. He grew them with his family and they turned out to be dưa hấu (watermelon) seeds and were delicious. He continued growing a garden and using the watermelons, sent a message out to sea for rescue.
Word spread to the king once the king ate a slice of dưa hấu. He realized the person growing them was his son and quickly gave him permission to come back to the kingdom and forgave him. Dưa hấu was then grown at the kingdom in Mai An Tiêm's honor.