Mysha, these are all Englich titles. In Scotland William should be William lV although as a republican (Scottish) I couldn't care less.
Watching the marriage ceremony I was struck by the wording of the vows, all about honesty and Christianity and thought that Prince Charles must have taken those vows also and yet, the future head of the Church of England was sleeping with Camilla before, during and after his marriage to Diana. Just a thought