It has always been understood that Duchess Camilla would be called the Princess Consort when her husband Prince Charles takes over the throne while her step-daughter-in-law Kate Middleton would be known as the Queen Consort when her husband Prince William becomes King. However, it seems that it's not that simple and Kate wouldn't be able to have the Queen title if Camilla is called Princess.
It is a well-established constitutional convention in Britain that the wife of a King is styled as Queen Consort. However, the late Prince Philip, spouse of the current monarch Queen Elizabeth II, was known as the Prince Consort. The last time the country crowned a Queen consort was back in 1936, when Elizabeth, later known as Queen Mother acted as consort to her husband, King George VI, until his death in 1952.
However, the future of the title Queen Consort remains uncertain due to the lasting impact of Princess Diana's death on the British monarchy. Diana was due to become the Queen Consort, and continued to be referred to as the Princess of Wales even after her divorce from Prince Charles and her subsequent death. This was the reason why when Camilla married Prince Charles in 2005, she didn't start using her automatically inherited Princess of Wales title and stuck with the lesser Duchess of Cornwall honour out of respect for Diana.
At the time of the marriage, Buckingham Palace clarified that Camilla would be known as the Princess Consort when her husband becomes King. There are also speculations that Prince Charles will push for her to get the Queen title. His apparent wishes could potentially be fulfilled, as major constitutional changes would have to be made if the palace wants Camilla to be called Princess and not Queen.
Camilla will automatically become Queen Consort when Prince Charles ascends to the throne unless legislation is enacted by parliament to the contrary, which would be a constitutional nightmare. Just to change the title of the wife of a King, the House of Commons and the House of Lords would have to work to pass legislation, as would the legislative bodies of other Commonwealth realms.
If this legislation does pass, it is possible that the parliament won't try to revert it in just a few decades when Prince William becomes King. It means that there may never be a Queen Consort in the UK again, with all future wives of Kings, including Kate Middleton, being styled as Princess Consort.
Royal historian Marlene Koenig told Royal Central that any move to make Camilla Princess Consort could "set a terrible precedent" for the Duchess of Cambridge. The author explained, "When Charles dies and William succeeds, there could be an announcement that Catherine will be styled as Princess Consort."
He added, "Will this happen though? I don't think so. Camilla should be styled as Queen Consort. The past is the past. She will be the wife of the King and she remains an active member of the royal family."