After Sirius was exonerated, he and Remus made a quick stop to Little Whinging to pay a visit to Petunia and Vernon Dursley. Coincidentally, their trip fell on the same day as the full moon, and they couldn't help that the wolf was close to the surface. Needless to say, after a visit with Moony and Padfoot, the Dursleys didn’t put up any arguments, and swiftly signed over their custody of Harry. They packed up what little possessions he had, and brought him back to Grimmauld. Harry was officially Sirius’ legally adopted son, and heir to both the Houses of Potter and Black.  