Eris, goddess of discord was angry at not being invited to the royal wedding.
Eris threw a golden apple at the guests to see who was the fairest of them all.
Hera, Athena, and Aphrodite all thought they were the fairest.
Zeus would not settle the dispute so he he had Paris settle it.
Let Paris decide who is the fairest of you all.
Paris was raised as as a shepherd because it was prophesied that he would be the downfall of Troy.
For the apple, Hera told Paris she would make him the king of Europe and Asia, Athena offered to lead Troy to victory against the Greeks, and Aphrodite Promised him the most beautiful woman in the world. He chose Aphrodite.