The PH talks about elvish blood in the half elven section. To quote:

"The relationship between elf, human, and half-elf is defined as follows:
1) Anyone with both elven and human ancestors is either a human or a
half-elf (elves have only elven ancestors) 2) If there are more human
ancestors than elven, the person is human, if there are equal numbers or
more elves, the person is half-elven."

BTW - that means that if Fhillaraene's brat gets born in Taurhievel and the
line remains strictly hereditary, there will never be another full blooded
elvish ruler.

l8r
Tim