The College of Arms:
The Titles of HRH The Prince Philip, Duke of Edinburgh
The Duke of Edinburgh was granted the style and title of Royal Highness on 19 November 1947; on the next day, 20 November, he was created
Duke of Edinburgh, Earl of Merioneth and Baron Greenwich, of Greenwich in the County of London.
These peerages are hereditary and on the death of His Royal Highness have passed to his eldest son, HRH The Prince of Wales. In the event of the Prince of Wales or any subsequent holder of these titles succeeding to the Crown, these titles and all others held will merge with the Crown.
His Royal Highness was made a Prince of the United Kingdom by Letters Patent of the present Queen dated 22 February 1957. A declaration of the same date communicated Her Majesty’s will and pleasure that her husband be known as
His Royal Highness The Prince Philip, Duke of Edinburgh.
His Royal Highness’s style and titles will be declared at his funeral by Garter Principal King of Arms, in accordance with custom.
https://www.college-of-arms.gov.uk/news-grants/news/item/187-hrh-the-duke-of-edinburgh