Personal unions can arise for very different reasons , ranging from near coincidence -LRB- a princess who is already married to a king becomes queen regnant , and their child inherits the crown of both countries -RRB- to virtual annexation -LRB- where a personal union sometimes was seen as a means of preventing uprisings -RRB- .

The case that a princess who is already married to a king becomes pregnant , and their child inherits the crown of both countries is a rather common cause .
