As per the comments, "twice removed" simply means two generations younger, or further down the line of succession. So the Queen Victoria's successor twice removed would be King George V.

Thank you very much for your answers! I really appreciate it.

The phrase "the present incumbent at Blackstable" could refer to the person who currently holds the job or the position in the organization called "Blackstable" that "my uncle" held in the past and then left. In that case, "my uncle's successor" is the person who filled the job or position after "my uncle" left the job or position. "My uncle's successor once removed" would be the person who replaced "my uncle's successor", and "my uncle's successor twice removed" would be the person who replaced "my uncle's successor once removed". Depending on the job or the position, it is not necessary for one person to die before the successor assumes the job or position.

Salaam Mehrdad. Khubi? Following on from John's answer, the successor twice removed would, I think, mean two people distanced from the successor of the person who died - this means the successor would need to die as well, plus the successor once removed, and then the successor twice removed would take up the position.

Each removed equals one generation. Or one step back down the family tree. Not in relations to first and second cousins but when working out a generation with only one common ancestor, grandparents. See the video in the page in this link. https://www.livescience.com/32121-whats-a-second-cousin-vs-a-first-cousin-once-removed.html It used to be a term I heard often when I was younger, but not so often now because it can get a little complicated to follow. Imagine a family tree first and second cousins are separated vertically, once and twice removed cousins are separated horizontally. Another term to use is the other side of the family. Meaning you come from the grandmothers or grandfathers side and only meet with a common grandmother and grandfather further back in history. This is the easiest way to visualise it.