HRH Prince Philip of Greece, the United Kingdom of Great Britain & Northern Ireland, & Denmark, Duke of Edinburgh, Earl of Merioneth, Baron Greenwich - a short bio.
10 June 1921 - HRH Prince Philip of Greece and Denmark is born on the Greek island of Corfu to HRH Princess Andrew of Greece and Denmark (formerly Princess Alice of Battenberg). He is a nephew of HM King Constantine of Greece, and is 7th in line to the Greek throne. Through his mother, Prince Philip is a great-great-grandchild of Queen Victoria of the United Kingdom, and therefore a descendant of Princess Sophia, Electress of Hanover. His father is HRH Prince Andrew of Greece and Denmark. As a Greek prince, Philip is styled as His Royal Highness; this takes precedence over his style of His Highness as a Prince of Denmark. In Denmark only children of the Sovereign and children of the heir apparent are styled HRH; Philip is neither. However, his is 15th in line to the Danish throne.
4 December 1922 Prince Andrew and his family are banished from Greece, and are evacuated by the British cruiser HMS Calypso. The family became dispersed, with Prince Philip's father in France, mother in Switzerland, and elder sisters in Germany. Prince Philip is brought up in Britain by his Battenberg relatives, who have adopted the surname Mountbatten.
27 July 1932 King George V revokes the Royal Warrants that had allowed the use of foreign dignitaries and titles by British subjects.
16 July 1942 Prince Philip is commissioned as a Lieutenant in the Royal Navy .
28 February 1947 It is noted in the London Gazette that Prince Philip is naturalized as a British subject; as is standard procedure for the naturalization of a title foreigner, he is by law informed that his foreign title will not receive official recognition, and is asked specifically to acknowledge his acceptance of this. He therefore becomes within the United Kingdom a commoner, namely Lieutenant Philip Mountbatten R.N., taking his adoptive family's surname.
9 July 1947 The engagement of Lieutenant Mountbatten and HRH The Princess Elizabeth is announced with Royal consent.
19 November 1947 Lieutenant Mountbatten is created a Knight Companion of the Most Noble Order of the Garter by King George VI and granted the style His Royal Highness. He is therefore within the United Kingdom now HRH Sir Philip Mountbatten, K.G.
20 November 1947 Sir Philip is made the Duke of Edinburgh, before marrying Princess Elizabeth that same day; he is now HRH The Duke of Edinburgh. He is also granted some lesser British titles; Earl of Merioneth & Baron Greenwich. This being an Anglican marriage, he is no longer Greek Orthodox and is therefore excluded from the Hellenic succession.
19 December 1947 As there is some confusion as to the fact that the Duke of Edinburgh is styled His Royal Highness but lacks the royal dignity of Prince, the Garter Principal King of Arms sends a letter to the Lord Chancellor's office stating that "There is I think a general idea that the Duke by virtue of his H.R.H. has become a Prince of the United Kingdom, but in fact I believe he remains a Prince of Greece and Denmark though naturalized here."
27 March 1953 The Danish Act of Succession restricts heirs to descendants of King Christian X, removing the Duke of Edinburgh from the line of succession.
5 December 1956 An Appellate Committee of the House of Lords passes judgement that the Sophia Naturalization Act 1705 grants British nationality to all descendants of Princess Sophia, Electress of Hanover; this affects over 400 people across Europe, including members of every Royal House bar one. The successful applicant is HRH Prince Ernest Augustus of Hanover. The Duke of Edinburgh is one of those affected; his previous naturalization is moot, as he was from birth already a British subject, and he is entitled to all his royal titles in their relevant jurisdictions.
8 December 1974 After returning to democracy, Greece votes to abolish the monarchy and become a republic, confirming the results of previously illegal referenda that had been organized by the military junta that overthrew the monarchy in December 1967.
12 October 2001 in the Danish Folketing confirms that descendants of King George I of Greece (grandfather of the Duke of Edinburgh) are titled Prince of Greece and Denmark, and as they are descendants of King Christian IX of Denmark they are eligible for Danish passports.
Conclusion
Prince Philip has been from birth entitled:
HRH Prince Philip of Greece and Denmark; being
HRH Prince Philip of Greece, and
HH Prince Philip of Denmark
However, these titles have had no official recognition within the United Kingdom since 27 April 1932. The Greek monarchy was abolished by referendum on 8 December 1974, so Greek royals are only acknowledged in Greece by their lesser Danish titles, which remain valid. Since his marriage he has also been entitled to the following titles, the only ones with which he has recognition in the United Kingdom:
HRH The Prince Philip, Duke of Edinburgh, Earl of Merioneth, Baron Greenwich