What is the story of The Tale of the First Calender, Son of a King?

The Tale of the First Calender, Son of a King is a story from the collection of tales known as Arabian Nights or One Thousand and One Nights. The story follows a young man who disguises himself as a beggar and sets out on a journey to discover the reason for his father's disappearance.

As he travels, he meets two other calenders, or religious hermits, and they decide to travel together. Each of them tells a tale of woe, and the First Calender recounts how he was once a prince who fell in love with a beautiful princess, but was forced to leave her to fight in a war. When he returned, he found that she had been forced to marry someone else.

The trio eventually arrives at the palace of a sultan, who is entertained by their tales and decides to grant them a wish. The First Calender wishes to marry the sultan's daughter, but the princess is already promised to another. The three calenders are then revealed to be the sultan's long-lost sons, and the story ends happily with the brothers reunited and the First Calender marrying his true love.