Sirius Black was a beautiful baby. When he was born, his family called him the bet looking Black there had ever been. From the first time he wailed in his mother's arms, he was instantly everyone's favourite. Mrs Black was proud to have given birth to a boy as perfect as little Sirius. They named him after the brightest star in the night sky, hoping that the boy would take after his namesake, and bring glory to the house of Blacks.
The first time Sirius Black befriended a Muggle from No. 10, Mrs Black was furious. However, she reasoned that Sirius didn't know any better, and that eventually he would learn not to consort with such lowly creatures as Muggles. But Sirius never learnt. Eventually, it was time for Sirius to go to Hogwarts, and Mrs Black was quite glad to get rid of him for some time: his mischievous ways around the house seemed only to have furthered with age, and he seemed to be making an active effort to bring disgrace to his Pureblood heritage. She hoped that once he was sorted into Slytherin, some sense would be knocked back in him. There was no question of him going to any other house: she wouldn't have it.
Mrs Black was ecstatic when Sirius sent a letter to her on the very first day back, for she was anxious to hear how the Slytherins had cheered when another Black had joined their ranks. However, he refused to tell her which house he had been sorted into, and instead ranted on for pages about a boy he had befriended named James Potter. At least the Potters were a Pureblood family, she thought, even if they weren't quite in the same range as the Blacks. She promptly wrote back to Sirius, asking him to tell her more about Slytherin house, eager to find out how her son had fit in.
Weeks went by without any correspondence from Sirius, and Mrs Black began to get more and more worried. Had Sirius not been sorted into Slytherin? Surely such a ghastly scenario was impossible. What if he had been sorted into Hufflepuff, or, God forbid it, Gryffindor? She would die of horror if her flesh and blood were put into that house of Mudbloods and Muggle Lovers. She wouldn't have it, she just wouldn't. Mrs Black wrote and urgent letter to Horace Slughorn, seeking reassurance that the Noble name of Black remained, to this day, unblemished.
Professor Slughorn replied with grim news, offerring regret at the fact that he hadn't, in fact, gotten the young Black for himself, and instead he had gone to Gryffindor. The rest of the letter, which offered great praise about young Sirius, was left unread. The next day, Sirius received a Howler at breakfast, and Mrs Black's shrill voice echoed all through the Great Hall, condemning Sirius for bringing shame to the Noble family of Black. "You have shown that you are no son of mine", she screeched, "and you will do well to keep you ill ways away from my Regulus. Never have I been as disappointed of a Black as I am of you today".
Young Sirius Black, only eleven at the time, burst into tears. He rushed from the Great Hall, having barely eaten, and was not seen for two days, for he had locked himself up in the Gryffindor tower. Eventually, hunger drove him out, and when Sirius stepped out of his dormitory into the common room, the entire Gryffindor house burst into applause. He had broken a trend, they chanted, he had ruined the false image of the Blacks, and shown that family history was no guarantee of one's ability. He had showed everyone at school that it was their choices, far more than their abilities, which made them who they were. James Potter ran towards Sirius and gave him a hug, whispering into his ear: "My parents always did want another child, and I have always wanted a brother".
Mrs Black would get letters upon letters from Sirius, droning on and on about his wonderful friends and classes and the lovely time he was having at Hogwarts. She would scan the letter once, looking for an apology from Sirius for disgracing the Noble name of Black, but she soon realised that it was not to come. Eventually, she stopped reading his letters altogether, and never once replied. In his fifth year, Mrs Black sent a letter to Sirius, saying that he did not need to come home for Christmas, that she did not want Regulus to spend a second more with him than was necessary. One year later, Sirius ran away from home, and though Mrs Black feigned outrage, she was glad that her family was free of the disgrace that was Sirius Black.
She blasted his name off the family tree, and neither of them ever heard from the other again. When she finally died and Sirius fell into inheritance of No. 12, he vowed to never set foot in that house again.