"Yes, Helga Crane. My mother was his sister, Karen Nilssen. I've been away. I didn't know Uncle Peter had married." Sensitive to atmosphere, Helga felt at once the latent antagonism in the woman's manner.
"Oh, yes! I remember about you now. I'd forgotten for a moment. Well, he isn't exactly your uncle, is he? Your mother wasn't married, was she? I mean, to your father?"

-Chapter 5 of Quicksand

Apparently the delineations of race and class supersede those of family.