I have a question about how royal and noble titles co-exist. The papers are all today reporting that the child will be titled HRH Prince X of Cambridge, or HRH Princess Y of Cambridge. I understand that is due to the Queen's Letters patent (issued earlier this year) that all of the children born to the Cambridges would be entitled to the HRH style and the rank and title of Prince / Princess of the UK. Without those special Letters Patent, the 1917 Letters Patent of George V would apply, and as a male line great-grandchild of the Queen the baby would only be styled as the child of a duke.
But if the child is a son, isn't he also entitled to use William's senior subsidiary peerage title - and in this case become HRH Earl of Strathearn? Edward's son is Viscount Severn - if he had been allowed to adopt his royal birthright and be known as a prince, would he still be HRH Prince James, Viscount Severn?
Or is the overriding rule that if you hold a royal princely title by birth, than you don't also add a courtesy peerage title to the end of that?