As he has said before, "almost all pure-bloods are somehow related, and he’s no exception". He’s related to the Weasleys by way of Cedrella Weasley (née Black), whom married Septimus Weasley. Together they're the paternal grandparents of the Weasley children. He’s related to the Malfoys through Narcissa Malfoy (née Black) who married into the Malfoy family, and is Sirius’ cousin. He’s even related to his godson, Harry Potter, through Dorea Potter (née Black) who is a distant relative to Harry and James Potter. 