Harry has always been in the line of succession to the throne. Before William had children he was number 3. Now he is 7; and will move up to 6 when the Queen passes, unless Parliament decides to remove him. Which would reignite an international fight about race.
Pardon, Harry is number 6 in the order of succession, and will be 5 when the Queen passes, unless William has another child in the meantime (he’d better hurry up!).