tethys-the-aquatic-sea-godness:

Sons of House Black: Marius Black

Marius Black was the third child of Cygnus Black II and Violetta Bulstrode, and brother of Pollux Black, Cassiopeia Black, and Dorea Black. Marius was disowned and removed from the Black family tree tapestry
for being born a Squib.
The Blacks were ashamed of his status, as Squibs are considered
second-class citizens in the wizarding world and disregarded.