How would the niece of my grandfather's cousin be related to me?

Yes, you are related but you only share about .78% blood relation. She is actually your second cousin once removed. Honestly, you can keep calling her your aunt as a term of endearement. This part of geneology is confusing, and I actually had to look it up. Check out this site if you want to know more: http://funadvice.com/r/1512jkp9ckm

only 78 percent. Wow! that is too much for me lol. Thank you for the answer.

no, she said .78%, less than 1%, so that’s barely related

Oh yeah I didn’t see that , thank you for the answer.

Annie has it almost right. First thing to point out is that your relationship to the niece of your grandfather’s cousin is the same as to the daughter of your grandfather’s cousin, because she is the daughter of another cousin of your grandfather (brother or sister to the cousin you have in mind).

This niece (or daughter) is your third cousin, once removed. Why? Because when the “cousin” relationship comes from one of your parent’s siblings, it is your first cousin; when it’s from one of you grandparent’s siblings, it’s your second cousin; and when it’s from one of your great-grandparent’s siblings (as in this case) it’s your third cousin. If the cousin is of the same generation as you (aunt or uncle’s child; great-aunt or great-uncle’s grandchild; great-great-aunt or great-great-uncle’s great-grandchild), there is no “remove,” but for each generational step of difference, they are once removed. Here, you are the great-grandchild of one sibling, and the niece/daughter is the grandchild of the other sibling, so that’s one remove. Hence: third cousin, once removed.

If you find it hard to follow my description, just draw a family tree. It will seem much less complicated than it sounds, when you can actually see it.

P.S. I just followed Annie’s link, and I see what makes it complicated. See where that page says “Generations to common ancestor: 4”? That’s why I said she’s your third cousin, despite the page saying second. (Three generations to a common ancestor would be your second cousin; two generations to a common ancestor - your grandparent - would be your first cousin.) The problem is that its 4 generations from you to your common ancestor, but only 3 generations from her to that same ancestor (which is what “once removed” means). So if the rule is to always count the lesser number, that site is right about second cousin - but then it’s wrong about 4 generations. Can’t have it both ways.

I’m sure everything is all crystal clear to you now, right? Lol!