HM The Queen, the Horse whisperer, horses and dogs.

[creagdhubh]

Off topic, but who can blame you?!! That must have been special indeed.

***!!!

[Deirachel]

He was made a Knight of the Garter, then His Royal Highness, before he was created Duke. In that order.

The pertinent announcement in the London Gazette. (requires a PDF reader) Note, it's listed before the Announcement of his Titles. (Very bottom of the page, top of the next.) Additionally, compare HRH's name as listed in the first announcement then to the second announcement.

"Lieutenant Sir Philip Mountbatten, K.G., R.N., shall be entitled to hold and enjoy the title, style and attribute of ROYAL
HIGHNESS."

then his name in the next announcement:

"Lieutenant His Royal Highness Sir Philip Mountbatten, K.G., R.N."

Therefore, HRH was made a Knight Companion before he was given the style Royal Highness, then was awarded his Dukedom.

And, I did specifically mention he was made Prince in 1957. Nevertheless, he was still "His Royal Highness" well before he was a Prince of the United Kingdom, and in fact, was HRH before he was duke.

Additionally, from the official website of the Royal family:

"Shortly before the wedding, the bridegroom was created Duke of Edinburgh, Earl of Merioneth and Baron Greenwich with the style of His Royal Highness and appointed a Knight of the Garter by the King."

Sorry.

[Mike_Oettle]

Well, Deirachel, it seems I was much too reliant on sources that did not state these further details. My thanks to you for the link to the London Gazette.
I should mention, though, that when I looked Prince Philip up on the royal website, I found no reference to his Garter knighthood being awarded in the year of his marriage, and mention of him (following his resignation of titles previously held) only as Lieutenant Philip Mountbatten, RN.
Regards,
Mike