"Will this cause a crisis for the British monarchy?" Well no because the British monarchy in truth only dates from 1707. Prior to that from 1603 Scotland and England shared a monarch. Great Britain was created through an act which lay down specifically who was heir to the throne of the newly created kingdom. That was Sophia of Hanover and her descendents. Sophia was the daughter of Princess Elizabeth Stuart of Scotland who herself was the eldest child of James VI of Scotland. In the Act of Union the Scottish Parliament accepted the succession as being that laid out by the English Act of Settlement. Prior to that they had suggested that they may choose a different monarch as long as they were also of the Scottish royal line and were Protestant. In other words they were offering the throne to the exiled Pretender as long as he gave up his Catholicism. The line of Richard III would have been of no interest to the Scots and without the Scots there was no Great Britain. Some could say that Richard's descendents would have been the rightful Kings of England but after 1707 that kingdom no longer existed anyway.