Harry Potter was born as the 7th month died, but also as the 8th began. This means that even before the first step of the prophecy began the Potters already believed that Harry's twin would become the saviour of the wizarding world. Dumbledore had obliviated the potters into thinking that they had made Sirius into their secret keeper as he wanted the seat that Black held but couldn't just murder him outright. Harry was in Sirius' arms after the street blew up and was somehow also suspected to be a death eater. After spending 10 years in Azkaban he is finally allowed to get his education and discover more about the world that imprisoned him.