My Brother's Son [Harry Potter Fanfic]

Regulus Arcturus Black and Sirius Orion Black are brothers. One was a Slytherin, while the other was a Gryffindor. One followed their parents' Pureblood ideals, while the other did not want to be a part of that. As they got older, the brothers' relationship became strained when Regulus decided to join Lord Voldemort and become a Death Eater. However, Regulus' time as a Death Eater revealed the horrifying extent of Lord Voldemort's ambitions, shattering his illusions.

Regulus discovers Voldemort's secret to immortality-a Horcrux-and decides to destroy it, sacrificing his life and ensuring his family's safety by commanding their house-elf Kreacher to remain silent. His act of bravery and selflessness would have been his end, but fate had other plans.

Regulus is unexpectedly transported 12 years into the future, landing in 1991. He learns that Lord Voldemort was defeated by a boy named Harry Potter in 1981, two years before he took his life. He is also shocked to learn that his brother Sirius was imprisoned in Azkaban for allegedly betraying his best friend, James Potter.

Stranded in this new timeline with no way back, Regulus adopts the disguise of Eduardus Regulus Black, posing as his brother's 'illegitimate' son, to uncover the truth behind these events and clear his brother's name.