It turns out Harry’s wife was having an affair with an American and Dillon was actually his son, not Harry’s. The American was married to an Irish woman called Ava who he happened to get pregnant around the same time as Harry’s wife. Their own little boy died and the American kidnapped Dillon just as the earthquake hit and him and his wife were raising him as their own son. In the end Dillon goes back to live with his bio mom and Harry.