Regulus Arcturus Black...

The younger brother of Sirius Black, with the purest and most innocent heart of the Black family, Regulus was always kind, kind to every living being that was near him

Sirius had a daughter, automatically Regulus became an uncle, uncle of a beautiful Black girl, but soon Sirius left Horgwarts, and Regulus knew nothing more about his brother and his niece...

Years later

Sirius and Regulus met at their parents' funeral, ending up fighting, Regulus furiously went out to the garden to try to calm down, however he didn't realize that the grass was too slippery, until too late when he fell into the black lake, a creature pulled him by the ankle, sinking him