How did Sirius get the Grimmauld Place? Common Law Ref.

[a_svirn]

No: HPFGUIDX 131754

Emma:
> The trouble with the entail theory, which does ring true in terms 
of 
> how Sirius might have inherited the Black estate, is that 
Grimmauld 
> Place itself seems to have been his mother's house, not his 
> father's, and therefore, self-evidently, had either descended 
> through the female line, or had been bought by Mrs Black with her 
> own money. If it had been inherited by Mrs Black, it could 
therefore 
> be passed on to another female. If she had bought it with her own 
> money, it would not be encumbered by an entail, and she could 
leave 
> it how she wished.

a_svirn:

Yet the tapestry represented the "Noble House of Black", and the 
portraits were also Blacks. Considering Sirius's bitter comments on 
the subject of the Black's inbreeding tradition and their conviction 
that being a Black makes one almost royal, my guess is that Mr and 
Mrs Black were first cousins (to marry a daughter off to a heir 
apparent in order to secure her inheritance was a practice not at 
all unheard of). Another possibility that the marriage was actually 
incestual. Blacks had been dark wizards for centuries after all, who 
knows what ghastly customs would that "entail".