King Aegeus was upset. When Crete demanded a human sacrifice to feed to the Minotaur, his son, Theseus, had gone. He loved his son dearly. Aegeus told Theseus to change the sails on his way back to let him know that his son was safe.
Theseus arrived in Crete, determined to slay the Minotaur and return safely.
Theseus met Ariadne. Ariadne fell madly in love with the prince and agreed to help him kill the Minotaur and escape the labyrinth in exchange for being married to Theseus.
Theseus, who didn't share Ariadne's feelings, left her on Naxos while she slept. Ariadne went on to marry Dionysus.
Theseus, in his celebration, forgot to change the sails to white sails. King Aegeus, upon seeing the black sails, killed himself.