Prince Philip was not given the title king of England during his wife Queen Elizabeth II's seven-decade reign due to longstanding royal rules.

Prince Philip -- who died at age 99 in 2021 -- renounced his royal title as prince of Greece and Denmark and became the Duke of Edinburgh after marrying then-Princess Elizabeth in November 1947.

When Queen Elizabeth ascended the British throne in 1952, Prince Philip was elevated to prince consort rather than king consort.

According to Reader's Digest, this is due to British Parliamentary law, which dictates that men who are married to the ruling monarch are not eligible to be named king or king consort.

There are different rules for men and women who marry into the royal family.

Unlike their female counterparts, men who marry into the royal family cannot take on the male form of their wife's title.

Queen Elizabeth II, Prince Philip, Duke of Edinburgh
Queen Elizabeth II sits with Prince Philip, Duke of Edinburgh as she delivers her speech during the State Opening of Parliament in the House of Lords at the Palace of Westminster on June 4, 2014 in London, England. Ray Collins - WPA Pool/Getty Images

For example, Princess Eugenie's husband, Jack Brooksbank, did not get a peerage when they tied the knot in 2018, according to Town & Country.

But Kate Middleton became Duchess of Cambridge and Meghan Markle gained the title Duchess of Sussex after marrying Prince William and Prince Harry, respectively.

This rule also applies to spouses of monarchs.

A ruling queen's husband -- like Prince Philip -- is referred to as a prince consort, while a ruling king's wife can receive the ceremonial title of queen or queen consort.

While queen can be a symbolic title, only the male monarch who inherits the throne and reigns can use the title king, Town & Country noted.

Prince Philip
Lieutenant Philip Mountbatten, prior to his marriage to Princess Elizabeth, saluting as he resumes his attendance at the Royal Naval Officers School at Kingsmoor, Hawthorn, England, July 31, 1947. PNA Rota/Keystone/Hulton Archive/Getty Images

Queen Camilla became queen consort after her husband, King Charles, ascended the throne upon the death of his mother, Queen Elizabeth, in 2022 and was crowned alongside him the following year.

Princess Kate is also expected to be referred to as Queen Catherine when Prince William becomes king someday.

On the other hand, Prince Philip was not crowned alongside Queen Elizabeth during her coronation ceremony in 1953.

Queen Elizabeth later made him an official prince of the United Kingdom in 1957.

Queen Elizabeth II, Prince Philip, Duke of Edinburgh,
Britain's Princess Elizabeth (future Britain's Queen Elizabeth II) and Prince Philip The Duke of Edinburgh pose in Buckingham Palace, in London in 1948. AFP via Getty Images

Prince Philip was the fifth consort to a ruling queen in British history, following King Philip II of Spain, William III, Prince George of Denmark and Prince Albert.

Prince Philip died at Windsor Castle in England on April 9, 2021, one month before his 100th birthday.

Queen Elizabeth II passed away at age 96 at Balmoral Castle in Scotland on Sept. 8, 2022, just a few months after celebrating her Platinum Jubilee.

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Prince Philip, Queen Elizabeth II, Queen elizabeth