Dav Ito (they/them) quoted Winter Lost by Patricia Briggs (Mercy Thompson, #14)
Content warning CW for incest, Spoiler for Winter Lost plotline
"She feeds on it, and it feeds on her--as long as she is married to a member of the family."
"Are we talking about 'I am my own grandpa'?" said Adam somewhat obscurely. "Let me guess, she is also Andrew's great-grandmother."
"Great-great-grandmother. But she was also that husband's great-grandmother." Liam sighed. "She's been marrying her own descendants every few generations."
— Winter Lost by Patricia Briggs (Mercy Thompson, #14) (71%)
Faeries are crazy, but I suppose when immortality and magic and power are on the line, humans can be pretty crazy too.