Charles will be the second monarch in a row who will have a tricky time figuring out what the official title of his consort should be. Queen Elizabeth's husband went through a weird in-between period early in her reign where he was a "His Royal Highness" but not a "Prince," and since 1957 he has been Prince Philip, Duke of Edinburgh, but doesn't hold the formal title of Prince Consort that was created by Queen Victoria for her husband Prince Albert. It's been complicated.
When Charles ascends the throne, he's going to have a bit of a conundrum on his hands, too. Technically speaking, the wife of a king is always the queen consort. However, because Charles and Camilla have a complicated history in the public eye, no one is actually sure what she'll be called officially. The title "Princess Consort" is the mostly likely title. But just as Camilla is, technically, the Princess of Wales now (even though she never uses the title), she will, technically, be the queen when Charles is king.