Yes, there are likely some fanfictions out there with that concept. You can try searching on major fanfiction platforms like Archive of Our Own or Fanfiction.net.
I'm not certain if there is a specific, well - known fanfiction with this exact premise. But considering the creativity of the fanfiction community, it's very likely. The idea would bring a whole new dynamic to the Harry Potter universe. It could involve exploring how Harry's character would be shaped by the different personalities and backgrounds of Regulus and Severus, and how it would affect his relationships with other characters like Dumbledore, Ron, and Hermione.
It could be full of family secrets and revelations. Harry might discover his true heritage in a dramatic way and have to deal with the implications of being related to Regulus.
There might be some out there. You could try searching on fanfiction websites like Archive of Our Own. Just type in 'Harry is Regulus' son' in the search bar, and you'll likely find relevant stories.
Harry is the central figure. However, Bellatrix Lestrange could be an important character in a different sense. As a Black, she might have some connection to Regulus and thus to Harry. And then there's Hermione. As Harry's friend, she would be there to support him through the revelations about his parentage. Her intelligence and loyalty would be key elements in helping Harry deal with the situation.
One possible plot twist could be that Harry has hidden magical abilities passed down from Regulus that no one expected. Maybe he can communicate with certain magical creatures in a unique way.
The plot could start with the discovery of Harry's true parentage. Maybe there was some sort of magical interference or secrecy spell that kept it hidden. Then, Harry might struggle with his identity, having grown up believing he was the son of James and Lily. He could also face different reactions from the wizarding community, some being accepting and others being hostile due to the unexpected nature of his parents.
A plotline could involve Harry's discovery of his true parentage. Maybe he grows up thinking he's just James' son, and then finds out about Regulus. This could lead to a journey of self - discovery, as he tries to understand the parts of himself that come from both his fathers. He might also face opposition from some in the wizarding world who can't accept this unusual family situation.
Well, in such fanfictions, it could be that the author invents new prophecies or backstories. They might say that there was a mix - up at the time of Harry's birth, and that he was actually Regulus's son all along. Or perhaps there are some items or memories that only make sense if Harry is related to Regulus, like a locket that has a special connection to both of them.
At first, it might be a bit of a rocky start. Harry, having grown up without a proper family, could be wary of Regulus. But as time passes, he starts to see Regulus as a father figure. Regulus, on the other hand, is determined to make up for his past mistakes by raising Harry right. So he showers Harry with care and magical knowledge, and they gradually form a strong bond.