What about the younger children of the future King George V who were born in the reign of Queen Victoria, while their father was the Duke of York? Was the man we know in history as King George VI born with the title of Prince, but with the qualification of only Highness? I know that his older brother, the future King Edward VIII, was styled from birth as a Royal Highness.
Before, I believe the niece and nephew of King George III through his brother, the Duke of Gloucester, were born to the rank of Highness, with William being elevated to Royal Highness later on, after marrying his first cousin Mary, a princess who was one of the six daughters of his sovereign uncle.
Have these been the only instances where the rank of Highness applied?
Elsewhere, it has been said that in Denmark the qualification of Royal Highness applies only to the children of a sovereign and grandchildren through eldest son of a sovereign. Of course, since the second son of King Christian IX got elected as King George I of the Hellenes, all his own children would have been Royal Highnesses -- even being styled with the title Prince(ss) of Denmark. But what of the children of his youngest son, Prince Valdemar? Were they only Highnesses throughout their lives?
As for the future King Frederik VIII: I know that he was already a grandfather several times over, by the time of his accession to the throne in 1906. Was the future King Frederik IX the only grandchild of his born in the reign of King Christian IX with the rank of Royal Highness? Was Prince Knud born a Highness, elevated to Royal Highness later on, like the children of his uncle Harald?
I believe that even the man we know in history as King Olaf V of Norway was (like his cousin Knud) born only a Highness, as Prince Carl of Denmark -- son of the second son of the future King Frederik VIII. He got elevated to a Royal Highness in 1905, when becoming the crown prince of Norway, as his father (also born Prince Carl of Denmark, but to the rank of Royal Highness) got elected as King Haakon VII.
Is all this true? Can anybody clarify me on the rank of Highness? I know that in Russia, it applied to great-grandchildren in dynastic male lines of sovereigns. It also applied to cadet members of some sovereign houses which were not kingdoms.
Case in point: Queen Amalia of Greece, consort of King Otto, was born Her Highness Duchess Amalia of Oldenburg -- a grand duchy, not kingdom. Only the sovereign, consort, and heir apparent to a grand duchy are styled as Royal Highnesses.
Of course, there are differences among the grand duchies, when it comes to the styles of cadet members. In Baden, they are Grand Ducal Highnesses. Ditto for Luxembourg, until the marriage in 1919 of Grand Duchess Charlotte to Prince Felix of Bourbon-Parma. I'm less certain about Mecklenburg ... Can anybody clarify?