Sirius' Cousin

Now, if I've got the family tree right:

Sirius + Bellatrix = cousins
Bellatrix + Narcissa + Andromeda = sisters, therefore
Sirius + Narcissa + Andromeda = also cousins
Andromeda + Nymphadora Tonks = mother and daughter, therefore
Sirius + Tonks = cousins

Just a little joke on what Sirius' reaction might have been finding out that his oldest friend hooked up with one of his cousins, enjoy!