I am the son of your grandmother and grandfather but not your uncle. Who am I?

Why this works

This riddle plays with family relationships to create a twist in understanding. The phrase "son of your grandmother and grandfather" suggests a direct descendant, which could imply a son or daughter of your grandparents. However, by stating "but not your uncle," it eliminates the possibility of it being your uncle—a sibling of your parent. This leads us directly to "your father," who fits the description perfectly as he is indeed the son of your grandparents but is not your uncle.