...So, for example, if Harry is created Duke of X, Baron of Y and Viscount Z, then:
- Harry will be known as Prince Henry, Duke of X
- His eldest son (and Heir Apparent) will be known as Baron of Y
- The eldest son of the eldest son will be known as Viscount Z
The subsidiary titles used in the above example are in the wrong order as Viscounts precede Barons in the peerage [Duke-Marquess-Earl-Viscount-Baron].
Based on the assumption that Harry becomes a Royal Duke and remains true to the Letters Patent of 1917, his eldest son will likely be born as a courtesy-titled Earl but later become a Prince of the United Kingdom with the style of Royal Highness.
So under the present convention and assuming Harry's eldest son is born during the reign of Elizabeth II it's more likely to be:
- Harry is created Duke of X, Earl of Y and Baron Z and is known by his ducal title
- His eldest son will be Earl of Y (courtesy title)
Duke Harry is unlikely to have a grandson during the current reign but if this occurred, the Earl of Y's eldest son would bear the courtesy title of Baron Z.
The situation would change on Charles's accesstion to the throne when the Earl of Y becomes a male-line grandson of the Sovereign and thus entitled under Letters Patent to be a Prince of the United Kingdom with the style of Royal Highness. He would be known as Prince ... of X.
- The Prince's eldest son (Harry's grandson) would likely be passed the courtesy title of Earl of Y
- The Earl's eldest son would in turn be known as Baron Z
Leaving the Wessex/future Edinburgh creation to one side, the current title conventions used within the Royal Family are straightforward. Best examples are for the two sons of George V who had male issue, namely Henry Duke of Gloucester and George Duke of Kent:
- The Duke of Gloucester (Prince Richard of Gloucester from his birth in 1944 until his father's death in June 1974)
- The Duke's son: Earl of Ulster (born October 1974)
- The Earl 's son: Baron Culloden (born 2007)
- The Duke of Kent (Prince Edward of Kent from his birth in 1935 until his father's death in 1942)
- The Duke's eldest son: Earl of St Andrews (born 1962)
- The Earl's son: Baron Downpatrick (born 1988)
There is clarity in the Gloucester and Kent titular flow. The immediate Royal Family's present situation muddies the waters due to the Duke of York having no sons, Prince Edward's stop-gap Earldom causing confusion, and William's Dukedom being freshly-minted but destined to be superceded.