In Which Sirius and Regulus Black Are Secretly Tom Riddle’s Children AU
1. Walburga Black and Tom Riddle had feelings for each-other in school. Walburga is married off to Orion. She isn’t happy with him, and while aware of Tom’s muggle ancestry, is impressed enough by the fact that he is trying to distance himself from it and fully embrace the Magical world that she still keeps in touch with him.
2. A few years go by, and Orion and Walburga still don’t have a child. Walburga goes to her old friend Tom, gets drunk with him while bemoaning her unhappy marriage to her cousin and one thing leads to another and Sirius is born. This repeats less than a year later (adding a colicky baby Sirius to her complaints) and Regulus is born. Walburga uses obscure charms on the tapestry to hide her sons’ paternity.
3. Only Walburga is aware of the truth about her sons, as, if it came out that she had birthed not one, but two children from an affair with a half-blood (even one descended of Slytherin) the best case scenario would be the boys would be sent away, and Walburga would be forced to actually bare Orion’s child. The worst case…no, it’s best she doesn’t think about it. (Tom/Voldy doesn’t know about the boys, as if he did, he’d claim them himself.)
4. Everything is going fine, and Sirius and Regulus look enough like their mother that she can pass them off as Orion’s sons. Until they start talking, and they instinctively use Parseltongue. Walburga keeps the boys away from the rest of the family as much as she can, until at last her father discovers the truth at a family dinner, and threatens to kill the two children (who are barely six and five years old). Walburga obliviates her extended family, in front of her frightened, crying sons.
5. That night, she impresses on Sirius and Regulus the need to keep their ‘secret language’ to themselves, saying that others would hurt them because of it. When they get to Hogwarts age she reveals the truth to them: Orion Black is not their father, and the both of them are the bastard sons of herself and Lord Voldemort.
6. Sirius goes into Gryffindor in hopes of burying his true heritage from the world. If he’d actually explained his reasons, perhaps Walburga would accept it as the fumbling attempts of a scared child to protect himself. He doesn’t, and it starts to drive a wedge between them. Regulus goes to Ravenclaw for the same reason as Sirius, wanting to get as far from being noticed as possible. It doesn’t really work.
7. Regulus, knowing that he would never be able to keep such a secret as his true heritage in the presence of the Dark Lord, does not become a Death Eater. Sirius also doesn’t join the Order of the Phoenix. Even if they are unknown and unacknowledged, even if they hate what the man who fathered them is doing, neither brother can stomach the idea of fighting against him, and even worse, of possibly committing patricide. (There’s also the magical backlash from killing your own family members to worry about.)
8. Walburga is not keen on either of her sons being out of her sight, and hates the idea of them getting further involved with James Potter and his new bride. Worried, she enacts her plan by trapping Sirius and Regulus in a portrait (after kidnapping and swapping Sirius with a golum that will look and act like him). She hides the portrait in her private sitting room, where even Orion doesn’t dare to tread. The day after James and Lily’s murders and Harry being left with Petunia, golum!Sirius is dragged off to the ministry in hysterics. No one realizes anything is off. (The Golum is keyed to Sirius’s Magic and memories at the time of its creation and thus able to act as he would and mimic his magic).
9. For nearly fifteen years Sirius and Regulus are frozen in time with only each other (and their mother until she dies). Anxious to free his masters, Kreatcher sneaks the portrait into Hogwarts, in the hopes that someone will free them. (The brothers are unable to tell anyone anything, as Walburga spelled the portrait to prevent anyone but her understanding what they say, as long as it’s a human language.)
10. Harry’s life continues as in Canon until third year, golum!Sirius escapes Azkaban, and Remus becomes the DADA teacher. The real Sirius is still stuck in the portrait with Regulus. The Ministry finally get wind of something being wrong with how the Dementors ignore Golum!Sirius when he is finally caught, and they realize that it isn’t actually Sirius Black, but instead a magical construct that was created before Harry Potter was even born.
11. About that time, Harry is wandering the halls when he comes across a portrait containing two young men who are hissing at each-other, one of whom looks exactly like the picture of Sirius Black in his photo album.
12. Before the night is over, the truth is revealed, and the Black Brothers are freed from their imprisonment. Sirius meets the godson he’d never got the chance to know about. Kreacher is thrilled to have Master Regulus back (less thrilled with having Master Sirius, but if it makes Master Regulus happy…).
13. Kreacher has been keeping Number 12 clean and ready for his masters, and they reluctantly return to their ancestral home. The Wizarding world is busy dealing with the shock, and Sirius and Regulus’s reluctance to explain why their mother hid them away.
Things continue as they would otherwise until after the Triwizard Tournament and regaining a body, Voldemort does a spell to find his nearest living kin for some reason, and Walburga’s sons’ names appear.