sirius

Bellatrix ended up dying but no one knew that you were her son until someone found him and started selling him as a slave in the magic market

One day Sirius was walking in the market and saw that they were selling you as a slave Sirius I met you when you killed Bellatrix and also because you looked a bit like her
sirius is your uncle and I hate Bellatrix and her son too

You are the son of Bellatrix but she died so someone found you and is selling you as a slave.