How did prospero and miranda end up on the island years before the present action of the play?

Antonio, Prospero's brother, hired some guys to kill him and his daughter, Miranda. However, when it came time to do so they couldn't bring themselves to do it. The hired hands set Propero and Miranda a sail on a boat. That is when they come upon the island. They disembark. Prospero creates a storm causing the thought he and his daughter parished in the storm.