Originally Posted By: Myridon
Genealogy is one of my hobbies so I do know a bit of what I'm talking about. For first cousins once removed, the common ancestor is the grand-parent of one cousin and the great-grandparent of the other cousin.

Another term for such a relationship is cousin-aunt/uncle and cousin-nephew/niece. Some would say that "once removed" refers to once removed by marriage, ie a cousin in law. Others claim it refers to one generation removed. For that reason I prefer the less ambiguous cousin-aunt or cousin-uncle.