Hi, cuz!

The recent story of the Queen shaking hands with Martin McGuiness has brought into focus the Queen's relationship with Earl Mountbatten, who was assassinated by the IRA.  I always thought he was her uncle - mainly because she used to refer to him as such, but it turns out they were cousins.  But what sort of cousins?  The rules on this are relatively simple, once you understand them.  So - the first thing you have to do is find the most recent common ancestor.  If you and X's most recent common ancestor is a parent, then clearly you are brothers and/or sisters.  If it's a grandparent, then you are first cousins - usually just referred to as cousins.  If it's a great grandparent, then you are 2nd cousins; a great-great grandparent, 3rd cousins and so on. But what if the common ancestor is a different relation to you both - your grandparent, but X's great-grandparent for example?  In this case the ranking (1st, 2nd, 3rd cousins etc) is determined by the closer relationship - in the example, a grandparent is a closer relationship than a great-grandparent, so you and X are first cousins of some sort.  You then look at the generational difference between the two relationships - here grandparent and great-grandparent are one generation apart, so you and X and first cousins once removed.  So how about the Queen and Earl Mountbatten?  Well their most recent common ancestor is Queen Victoria.  She is the Queen's great-great grandmother and Mountbatten's great grandmother.  So they are second cousins (great grandmother) once removed (one generation apart).  The Queen and Prince Philip, by the way, both have Queen Victoria as their great-great-grandmother, so they are 3rd cousins.