Srila Prabhupada is reported to have told this story, so I'll elaborate on it a bit. A twenty-five-year-old Vedic king was loved by his subjects, whom he treated like his own sons and daughters. He was chivalrous, expert, handsome, powerful and wise. Once upon a time a beautiful apple appeared in his quarters as often happens to people of his rank. The apple's shape was perfect, its fragrance intoxicating, its color unblemished crimson. It had a short stem, and two green leaves protruded from the short stem. It had an unmistakable uniqueness about it.
On seeing this natural specimen, the king immediately smelled it and gave it to the queen. Four hours later, a beautiful female subject presented the king with an apple, and the king realized it was the same one he had smelled earlier that same day. He immediately decided to take sannyasa, and began living in a remote forest.
You see, just after the king gave the apple to the queen, she gave it to her lover, who in turn gave it to his lover, who in turn gave it to the king, who happened to be her lover. The astute king figured all this out and hence decided to renounce the world.